E-file the return, then, within 3 business days of receiving IRS acknowledgement that your return was accepted, mail form 8332 (completed by your ex) along with form 8453 (search forms in Turbo Tax or online).
https://turbotax.intuit.com/tax-tips/family/what-is-form-8332-release-revocation-of-release-of-claim...
If you have custody of your child but want to release the right to claim your child as a dependent to the noncustodial parent, you’ll need to fill out Form 8332. All that’s needed is your child's name, the tax year, your Social Security number, then your signature and date. If you prefer to release your claim for more than one tax year, enter the same information in part two rather than part one. You also use the form to revoke a previous release of a claim.
Once complete, give the form to your child's noncustodial parent, not the IRS. They will file it with their tax return. If you release your claim for multiple tax years, you only need to fill out the form once: the other parent will attach copies of the original to their return each year.
