A big reason that he run his SNS is to gain interests.

--> One of the main reasons he runs his SNS is to attract followers.

To gain weight is easy, but to lose weight is hard.

--> Correct sentence~ ^^ Good job!~ ^^ 

Have you seen your neighbor recently?

--> Correct sentence~ ^^ Good job!~ ^^ 

I heard recently that she got into the college where she really want.

--> I recently learned that she was accepted into the college of her choice.

I can't control my son on my own.

--> Correct sentence~ ^^ Good job!~ ^^ 

She is only good at controlling her anger in front of strong person.

--> She is only capable of managing her anger in the presence of a powerful individual.

Fail of controlling diet is why he can't lose his weight.

--> He can't lose weight since he can't regulate his food.

He started to control diet after he was diagnosed with diabetes.

--> After being diagnosed with diabetes, he began to watch his diet.

He is just trying that without primary knowledge.

--> He is only attempting this without prior understanding.

I just did primary things though I entered a company last week.

--> Despite the fact that I joined a company last week, I only accomplished the basics.

There will be crucial announcement at six.

--> Correct sentence~ ^^ Good job!~ ^^