Do I have to sign anything to let my ex-wife's husband claim my child for the tax credit? Per legal agreement we claim on alternating years. We both remarried last year.

The divorce agreement states that we can claim the child tax credit on alternating years. This current year is her year and she wants me to sign a form saying her new husband can claim. Is this necessary? I am not claiming the tax credit per our agreement, I would assume she is fine to claim it without any additional hurdles.