As I assume GSTr 2 will not going to be implemented this year, so kindly take the return (CNT) for wrong bill, & add the new bill for client u missed. all is to be done in Ur next GSTr 1, & plz while adding bill put its original date mention in bill. in GSTr 1 u can add the bills of Feb dt in march return.
* as in amendment u cannot change the GSTn. of party
plz do not pass any entries of rectification in Ur books of account