Dear Minhthi1810
I haven't heard any native people said the sentence which was like you
And "Thank" is a verb, you have to say " I thank you" but not" I am thank you"( or sth like that)
But in the formal English, they usually drop the subject and I think you should correct like this: "Thanks (or thank you) for you gift."
The way to improve: I think you should always find out if the word is a verb, noun or a adjective before writing a sentence.
Claire