I'm learning English and need help. I'm a native Mandarin speaker from China.

"So I'm looking for an exchange partner."

This sentence begins with a coordinating conjunction (So) and is a dependent clause. It cannot stand as a sentence by itself.  The best way to correct it in this case would be to put a comma after China instead of a period.

"I'm a native Mandarin speaker from China, so I'm looking for an exchange partner."

Your writing is quite good, though!

It's so nice to receive your guidance.Tks so much!