Client needs to file 2020 returns to be eligible for 3rd stimulus payment. Their AGI was too high in 2019. Submitted returns yesterday and received error message that the returns have already been received, so a fradulent return has been sent. 

Since filing by mail is taking a year, they will not receive 3rd stimulus payment until next tax season. 

Can I e-file an amended return with a pdf attachment of form 14039 ? Or is snail mail the only option?