Chess is a fun and benefitcial game.

My correction is grammatically correct, but it would be better to use two sentences. Something like, "Chess is a fun game. In addition to the fun, it offers many benefits."

So what isare the chess's benefitbenefits of chess?

You could still use the possessive adjective, but it is awkward to pronounce. When forming a possessive from a word that ends in s, just add an apostrophe at the end.
So what are chess' benefits?

Secondly , it helps you to ve planned personplan ahead.

Thirdly, it helps you to begain self confidence.

So if we play chess we can have better personality.

This sentence is grammatically correct, but it is false. Personality is how you interact with others socially. Chess is not a very social game. It helps you think, but it doesn't help with your personality.

Chess is a fun and benefitcial game.

So what is thare chess's benefits/What are the benefits of chess?

Firstly, it helps you think right and quickquickly and strategically.

Secondly , it helps you to ve planned person well.

Thirdly, it helps you to bebecome confident/It helps you with self confidence.

So, if we play chess, we can have better personalityourselves.

Chess is a fun and benefitcial game to play.

So, what is thare cthess's benefits to playing chess?

Firstly, it helps you think right and quickquickly and critically.

I wouldn't say "right" because in chess, with so many possible moves to make, you can't expect one move to be the only "right" one. I prefer, 'critically' or 'logically'.

Secondly , it helps you to ve become a better-planned person.

I think there are other ways to phrase this. The argument from that you're trying to convey from what I understand is that because you have to plan your own moves in advance and you also have to know what your opponent is planning, it translates into real life when making plans. To me, saying "It helps you make better decisions" is an option.

Thirdly, it helps you to become more self -confidencet.

So if we play chess we can have better personalityimprove ourselves.