Is there a way to do T4s and work in sage for year of 2020 when the back up cant be found. 2021 has already been uploaded

SUGGESTED

I cant find a back up of Sage 2020 on my computer and the program has already been updated to 2021.  I still have entries to do for 2020 and T4s to do for 2020 etc.  Is there a way 2021 can be un-done or a way to still work in the calendar year of 2020

tks