You can see whether the dependent is still shown on your tax return or not by looking at form 1040 in the Dependents section near the top of the 1040. If the dependent is still there and you want to remove the dependent, you can go to the Personal Info section and edit the dependent and delete the dependent.
If you are the one who has the right to claim the dependent, you can leave the dependent on your return and print and mail it. The IRS will process it and send your refund and later in the year will request information from both parties who claimed the dependent to support their claim. Whoever had the right will get to keep any tax benefits resulting from the claim and the one who did not have the right will have to pay back any benefits along with possible penalties.