Claiming dependents every other year

Per my divorce decree myself and my ex husband claim our daughter on a rotating basis every other year.  He claimed her 2019 and I claimed her 2020.  He has gotten every single stimulus since they began even after I filled our 2020 taxes claiming her.  He also received the first advanced child care credit.  He’s certainly unwilling to work with me, so I haven’t the foggiest of notions of what to do to get it straightened out.  Can you help direct me.