I need to change my dependency on my tax form

If you have not filed the 2019 tax return, click on My Info on left side of the online program screen while accessing your 2019 tax return.  Edit your personal information to change your dependency.

If you have filed your 2019 tax return then you will have to amend the tax return to change your dependency.

An amended tax return, Form 1040X, can only be printed, signed, dated and mailed by you to the IRS or it can be e-filed if your original tax return was e-filed. The IRS will take up to 4 months to process the amended tax return. Wait until you have received the tax refund or the taxes owed have been paid and processed by the IRS before amending the tax return.

See this TurboTax support FAQ for amending a 2019 tax return - https://ttlc.intuit.com/community/tax-topics/help/how-do-i-amend-a-2019-return-in-turbotax/01/1238456