You would have to amend your return to make the change.  Amended returns must be mailed.  Once you start the amendment process, you can change your dependent status in My Info, click Edit by your name.

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...