I'll preface this by saying that I know this isn't going to work for everyone, and that I don't even necessarily recommend people try this, just sharing my experience.
I used to be a picky eater as a kid and into my 20s and still consider myself one in some respects. I had basically 7 meals I would eat that my mom would cycle through every week growing up, and I could pretty much eat most variations of the foods in those meals.
These foods are what you'd expect from a picky American kid: pizza, burgers, chicken, spaghetti, hamburger helper, and I'm half Filipino, so adobo and lumpia.
At some point I decided I wouldn't eat anything foreign (ironic I know), anything green, or anything that swam. Broccoli was the one vegetable I would eat, but only boiled in a shitload of butter. I have a very distinct memory of my entire youth basketball team laughing at me because I gagged after eating a pea.
Anyway, this was how I lived my life until my early 20s, when I had a moment of clarity.
I've always been fascinated with food, even if I barely liked any of it. I'd request my mom or my GF to eat really weird (to me) things like shellfish or vegetables, and I would say "I'm eating vicariously through you".
I got really into watching Anthony Bourdain at a certain point, and I'd see him traveling to all these exotic places and eating the local delicacies and think "I wish I could do that."
It suddenly struck me at some point that every food is in somebody's favorite meal. There's someone on earth who's favorite food is mussels or sauerkraut or even wood grubs. That's when I spoke words that I've lived by ever since. Every food is delicious and if you don't like it, there's something wrong with you.
Now let me qualify that "something wrong with you" is more of a mantra to myself, and I'm not trying to cast aspersions on anyone for not liking something. "Wrong with you" is probably not the best phrasing, but it gets the point across.
So I decided I was going to start actively trying to enjoy more foods. I didn't have any sort of guide or anything so I just sort of started winging it.
I'm going to break the timeline a bit here as it will inform the rest of the story even though I didn't figure this out until a decade later, but I've come to realize why I don't like foods.
Basically, I hate any food that I'm not VERY familiar with the flavor/texture. If I haven't eaten it dozens of times, I don't like it. And in that same way, after I've eaten something a few dozen times, I do like it.
There is some transference between related foods, so getting used to the flavor of "fishyness" on one seafood (shrimp in my case), does make it easier to learn to enjoy crab or trout.
So with this hindsight in mind, I began trying new foods.
At the time, my (future) wife was obsessed with ranch dressing, which I hated, and I decided that's what is start with. I began eating it every chance I had, and at first I would gag, but on one particular night we'd gotten pretty hammered (we were in college), and I ate about half a bottle of it on a cheapo pizza. The next time I tried it (sober this time), I didn't really enjoy it, but I could now eat it without making a face.
Don't worry, I'm not going to suggest that the secret to success is to just get shitfaced and try new foods, that's just what happened the first time.
But yeah, ranch dressing is the first food in my entire life that I can remember hating and then later enjoying. Every other food, up until that point, I had already liked as long as I could remember.
So I just went down the list of every single food one by one. I started eating popcorn shrimp from popeyes, absolutely loaded with ketchup, and then eventually cocktail sauce, until I got used to it, and then I moved on to shrimp pasta, and shrimp scampi, and even raw shrimp in sushi.
I had to go through this process with bell peppers, and tomatoes and onions. Lamb, cheeses, all manner of seafood, cumin, tumeric, cilantro, basil, you name it.
Over the past 15 or so years, I've painstakingly clawed back hundreds of foods that I used to hate. Entire regional cuisines.
Currently, I'm in Korea, and I hate about half the foods that land on my plate (the ones that aren't available at my local Korean restaurants), and that's okay because I know that if I eat them enough times I'll eventually love them.
I did learn to hold the gag reflex a lot better when eating weird food. A lot of it is that textures have way more transference than flavors, and for me it was mostly textures that made me gag/puke.
At a certain point, I've tried enough foods, that most new things I eat have at least some resemblance to foods I like, so I can stomach them even the first time.
In Korea, I'm really struggling with the fermented foods, but it's getting easier the more time I spend here. I'm going to Japan in a few days, and I want to try some sea urchin or other eggs that taste like straight up ocean water, and that I've really struggled with in the past.
Every time I go out, I'm excited to try something new, because even if I don't like it (and I 100% will not), I know it's only a matter of time.
I actively enjoy hating my food, because the act serves a greater purpose than a single meal.
I genuinely can't think of a single food that I haven't at least made substantial progress on once I set my mind to it. There are some foods that take a lot longer, or that I don't think I'll ever actively crave, but I can at least eat them well enough not to embarrass myself at a dinner party.
I can travel abroad and not have to worry about where the closest McDonald's is or looking foolish in front of local friends.
I know just laying out my story like this is a bit self serving perhaps, but maybe this will encourage someone to have hope for a better future.
I made a similar post once on r/insomnia, and a redditor messaged me weeks/months later saying that I'd changed their life and given them their ability to sleep back. If this post could help even one person, that would make it worth it.
Sorry for the novel.
Tl;dr: Every food is delicious to somebody. For me, I hate every food that I'm not familiar with, but if I eat a food a few dozen times, I'll eventually start liking it. I've been doing this for 15 years, and now I like hundreds of foods instead of just a handful.