Revocation of GST registration and filing of return

sir,
someone registered a firm in GST , and issued invoices started from serial no. 101.
he has filed nil GST returns from the month of registration- July 20 to Jan 21 and no returns were filed for the month of February 21 to may 21. so department cancelled the GST registration.
now he wants to revoke the cancellation of registration.
so please guide me what and how to do.
what would be the late fee and panelty.

thanking you