Prepare your taxes with your daughter as a dependent. You will not be able to e-file it. You will have to print and mail it. Include all forms needed, sign the return, and mail to the address on the first page of the printout. I also would include a letter explaining that your daughter was claimed by your ex and should not have been.
It will take a long time, possibly more than a year, but the IRS will contact you and sort out the return.
