I claimed my daughter (age 27) as a dependent. She lives at home, but made more than $4200. What should I do? (I took the standard deduction-in case that matters.)

If you have filed the 2019 tax return then you will have amend the 2019 tax return and remove her as your dependent.

An amended tax return, Form 1040X, can only be printed, signed, dated and mailed by you to the IRS, it cannot be 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.

To access your online tax returns sign onto the TurboTax website with the User ID you used to create the account - https://myturbotax.intuit.com/

Scroll down to the bottom of the screen and on the section Your tax returns & documents click on Show. Click on the Year and Click on Amend (change) return

See this TurvrboTax 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

YOu will need to get your amended return mailed to the IRS by June 15th. That's because you will be paying back some money to the IRS. If you wait, then on Jun 16th what you owe the IRS starts to accumulate interest.