You can only transfer into a new blank return so you would have to start 2020 completely over.
If you already started an online return you will have to clear it and start over to transfer again. How to clear and start over
https://ttlc.intuit.com/community/using-turbotax/help/how-do-i-clear-and-start-over-in-turbotax-onli...
For the Desktop program, to transfer again you have to start a new return, go up to File-New.
