The IRS will allow you to amend your return to claim your daughter as a dependent, as long as your ex-wife has not claimed her. But by doing so you would be in violation of the court order. The IRS doesn't care about the court order, but your ex-wife probably cares about it. From a legal point of view, you need to resolve that before you claim your daughter. You should probably check with your divorce lawyer before you try to claim your daughter.
If your ex-wife has already claimed your daughter, your ex-wife would have to amend her tax return to not claim your daughter in order to allow you to claim your daughter.
If you do decide the amend your return, go to the following link for instructions to amend a 2017 tax return that you filed with TurboTax Online.
https://ttlc.intuit.com/questions/4252204-how-do-i-amend-my-2017-turbotax-online-return
An amended return has to be filed on a special form, Form 1040X. It cannot be e-filed. You have to print it, sign it, and file it by mail. It takes the IRS up to 16 weeks to process an amended return.
Don't file the amended return until your first return has been accepted and you have received the original refund.
