Check if this sentence is correct and if not plz tell me the correction.

This isn't a sentence, but an introductory dependent clause. It could start a sentence if it is followed by an independent clause.

But as an introductory dependent clause, there is nothing wrong with it.

To expand upon the answers from Lewis and Jeff, here is an example of a full sentence using your introductory dependent clause.

If all of you don't know him, I will send a picture so you can recognize him when he arrives.