Ex wrongly claimed dependent got EIP but my income is below filing threshold

My ex and I have been separated since late 2017 and legally fighting over custody since Feb 2019. I have always had primary and at least 70% custody. We filed married jointly for 2018 and all credits went to his accounts. 
My ex claimed our child on his (married separate) taxes for 2019 and, as far as I know, received the economic impact payments associated. 
Personally my income is below the minimum amount to file so this year I filed with the non-filers website and have received an EIP payment for myself.  
I’ve read that in order to fix my ex’s mistake I have to now file a paper return and wait. Does anyone know how/if this will work due to my low income and his already receiving the EIP?