I opened a new return for this year and realized after e-filed that it is not linked to previous year returns. Can I now link it or redo the return by 'opening an existing return' button? Thanks
Unfortunately, if you didn't import the information from your previous year's return when you started you current year return, then there is no way to do it afterwards.
You can start a new return and transfer the information, but then you would have to redo your entire tax return. You would also end up with 2 returns for 2021, one that was filed and one that wasn't.