After you file

i have a question that is somewhat related since it deals with an amended tax return. was wondering if you might know. i filed my 2020 tax return already and got refund. the third stim was processed after it was filed so it was used to determine if i qualify for the the payment. i was $2k over the limit and did no receive it. 

 

However I never realized that i can file as head of household (i do meet the qualifications for it). I always thought it was a married person thing so never even looked into it. if i file as head of household and IRS accepts the return and process it, will they automatically go back and pay the third stim. I have tried since they made the stim payment to get an answer but can never get through to the IRS to ask them