You would have to amend your return to remove the dependent.  Personal Info, next to the dependent's name, click delete.  Amended returns must be mailed.  If amending your Federal return affects your State return, then you would have to also amend your State.

How do I amend a 2019 return in TurboTax?

https://ttlc.intuit.com/community/tax-topics/help/how-do-i-amend-a-2019-return-in-turbotax/00/123845...