Since your Tax Return has already been e-filed and accepted by the IRS, you will need to wait until it has been fully processed and you have either received your refund or your payment has cleared. Once your Tax Return has been fully processed, you can Amend it to take the Dependent off of your Tax Return. Keep in mind, you will receive the Full amount of your original refund that included the Dependent, and when you file the Amendment, you will owe back the portion of your refund connected with that Dependent.
Unfortunately, your Dependent will need to wait until your Amendment has been processed by the IRS before he/she files their return.
Check out the TurboTax FAQ below for details on how to Amend your return:
https://ttlc.intuit.com/replies/3288565