I completed my 2020 return on another friend's account and want to import the completed .tax2020 into my new turbo account. How do import it?

Online accounts are only good for ONE tax return.    Any attempt to enter other data will overwrite and destroy the original data.

You can't move it to another online account or upload it from your computer to online.  You can only download a .tax file and open it in the Desktop CD/Download program.  If you used the Online version then your friend's account is now your account.  He will have to start a new account for his now.  You can use this account going forward.  Like if you want to transfer this return into next year.