Can I add a dependent to my 2020 taxes if so how do I do that?

If you have NOT filed the 2020 tax return dependents are entered in the My Info section of the program.

If you have filed the 2020 tax return then you will have to amend the tax return that was filed to add a dependent.

An amended return, Form 1040X, can only be printed and mailed to the IRS if the original tax return was not e-filed. The IRS will take up to 16 weeks or longer to process an amended tax return.

Before starting to amend the tax return, wait for the tax refund to be received or the taxes due to be paid and processed by the IRS.

See this TurboTax support FAQ on amending a tax return originally completed and filed using the 2020 TurboTax editions - https://ttlc.intuit.com/community/amending/help/how-do-i-amend-my-return/01/27439