I have already filed my taxes for 2020 but i received a w-2 i wasn’t expecting how can i add that?

the return at this point can't be recalled. the IRS won't open e-filing until 2/12/2021. so you'll have to wait. if your return is rejected you can fix it and resubmit. if it is accepted you'll have to wait until it is fully processed and then file an amended return

If you filed, it is like dropping it into a mailbox - you cannot get it back.

You'll have to wait until your return is either accepted or rejected.

• If rejected, you can make any necessary changes.
• If accepted, you'll need to amend your return. 
• To avoid unnecessary delays, do not amend until your original return has been fully processed.  You will need to print and mail the amendment.  
• Allow 8-12 weeks for processing.

See this TurboTax FAQ for help with amending.