FA few minutes ago, I have watched a video of Ryan Trahan, an American YoutTuber.

Since you just watched it, you can say "I watched" instead of "I have watched"
The proper capitalization of the title is "YouTube, so you should capitalize the Y and the T

I really appreciate his videos and I find them useful to learn the English and improve my comprehension.

We would just say "learn English" not "learn the English".

In the video I watched, he tasted food at the 5 best restaurants in America.

We wouldn't really say that you tasted the restaurants. We would either say that "he went to the 5 best restaurants in America" or "he tasted food at the 5 best restaurants in America".

But it's not juste likelike he's just someone who doesn't like but can eat it:them.

Ryan Trahan literally hates ithem.

Here, your direct object refers to "vegetables" plural, so you should use "them" instead of "it".

The idea came from one of his friends who is a doctor.

"One of his friends" - friends should be plural since you are referring to a singular friend out of a group of friends.

And, asince vegetables are so important for his health, he saitold him to doget a tattoo.

In English, we would say you "get a tattoo", not "do a tattoo".

However, I haven't heard the complete story but. I think it must have been a pledge.

You need a verb for the first sentence. The current structure asks: "You haven't 'what?' the complete story". Here, you can say, "I haven't heard the complete story".

Nevertheless, even with his tattoo, he didn't eat more vegetables than before.

You can just say that he didn't eat more vegetables. The "than before" part is implied.

All that foris to saying that in the best restaurant in America, he will eat in (the last), you can onlyon't eat vegetables.

I'm not exactly sure what you were trying to say here, but I touched it up to be more natural.

It will be a revelation for him: iswill the best restaurant in America be able to make him love to eating vegetables?

The first restaurant he went to serves pizza.

The restaurant won the pricze of the best pizza in the world.

"Price" = how much something costs
"Prize" = an award you win

The atmosphere in the restaurant was really cool and the pizza as well as the otherall the foods he eatse looked delicious.

He went there with his father who love barbecues.

They ate the meal which was really tender.

It was a quitet restaurant so he was afraid to speak too loud.

"Quite" = to a certain degree
"Quiet" = silent

The cookersushi chef was cooking jusright in front of him, so it was pretty impressingve.

We would call the person who does the cooking a "chef". Here, more specifically, you could call them a "sushi chef".

There were many dishes, and they all looked yummy.

As a matter of fact, I don't really love the sushi but I'm sure iI would love the sushis in this restaurant!

The fifth and final restaurant and the last was the restaurant which proposes onlywas the one that only serves vegetables.

He wasn't sure that heh would like the dishes, but he did.

He loved almost every dishes that he ate.

He was proud of himself because he ate vegetables for the first time since a long time.

In English, we say that you are proud of yourself, or he is proud of himself.

When he go out fromleft the restaurant, he saw his doctor friend who asked him to doget the tattoo.

He was so happy, i. It was good to see that.

These should be two separate sentences because they express two completely independent ideas. Or, you could combine them with "and" - "He was so happy, and it was good to see that".