A client filed 2020 tax return with Form 1120 and was notified by IRS that the company's S Corp election was accepted and should use form 1120S.  Since he made tax payment for his 2020 tax already and would like to get the extra payment back.  How can I amended Form 1120 to Form 1120S? Can I file 1120X to reverse everything, and prepare 1120S?  Thanks.