its auto refund , if u have shown ur BE no. dtate amount corectly in GSTr 1, & the same has been shown in 3b under zero rate sale tallys . yes u can check for the same online on portal under services for any mismatch.
otherwise u have contact to ur Jurisdictional concerning officer with all ur related dcument , like export bill copy, copy if ur gstr 1 & 3b return , etc