see this link
https://www.msatp.org/fixing-the-error-how-do-we-solve-depreciation-mistakes/#:~:text=Changes%20that...
however 2003 is a closed year so 3115 is required.
you do have an option not to file 3115 and change nothing. you can't change the depreciation base or method for 2021 that would be computed using the old method. also, your depreciation recapture would be the larger of that taken or that allowable.
