[edited] You need to include form 5695 on your tax return to report the carryover, calculate that you can't use any of it, and carry it forward again. There are specific instructions on how to do this on the form, if you were filing by hand.
Go to the Energy Credits section of the Deductions and Credits page. Start the interview, answer "yes" that you "made improvements or had a carryover", answer all the qualifying questions, and leave the boxes blank for all the improvements (because you did not make them in 2020). You will eventually get to a question, did you have a carryover from 2019? Answer yes, and the amount.
