In the first place the father will have to print and mail his return. So he doesn't have to wait for you to amend. Even if you amend he has to mail since the baby's ssn has already been used this year.
How to amend a 2020 Online return
https://ttlc.intuit.com/community/amending/help/how-do-i-amend-my-turbotax-online-return/00/27577
