I am good at communicating with people, even I have not seenmet before.

"Seen" makes it seem that you've never physically seen something before. (i.e. I've never seen your sister because she's always in her room.) Generally, "meet" sounds better in this context.

However I was notn't always good at communicating.

For example, when I met my aunt after a long absenctime, she was surprised at my communicatingon skills.

"A long absence" is grammatically correct but sounds a bit formal. "A long time" is more commonly used.

I wasShe thought I did not like to talk to anyone.

A opportunity tohat changed my mind iwas entrance into aering high school.

WhilThe more I did it, the more my communications skill was gettings got better.

Now, I do not feel anythingnervous when I have to talk to someone.

"Feeling nothing" doesn't quite sound right in English;

Please correct this sentenceparagraph!

I am good at communicating with people, even those who I have not seen.

However I was not good at communicating, my communication skills used to be bad.

"However" is a transitional word at the beginning of the sentence, so it needs a comma afterwards.
The rest of the sentence I changed. You used "good at communicating" in the first sentence, and in the English language we try to avoid a lot of repetitiveness.

For example, when I met my aunt after a long absenctime, she was surprised at my communicationg.

In this scenario, we would rather say "after a long time" than a "long absence". You would say long absence here:
After taking a long absence from my studies, I re-enrolled at university today.

I was thought I did not like to talk to anyone.

AThe opportunity to change my mind ishat helped me was my entrance into a high school.

I changed this sentence to make it sound better. I think "helped me" is better than "change my mind", because you are talking about your communication skills improving, and anything that makes you improve obviously helps you.

Here's an example of where you would use change my mind:
You can't change my mind, I'm set on moving to Spain next year.

I didn't know anyone at the school, so I had to talk to my classmates by myself.

"by myself" isn't necessary here

WhilThe more I did it, the better my communications skill was getting better.s got.

Changed the sentence to sound smoother

Now, I do not feel anything toxious when I talk to someone.

if you "don't feel anything" when you talk to someone, that means you don't feel any emotion - happy, sad, scared, etc. Since you were talking about how your communication skills were bad but now they aren't, I put "anxious" instead.

Please correct this sentenceparagraph!

A sentence is just one line, a paragraph is a group of sentences :)