But yes you can amend if your return was accepted or mailed. Or is your return rejecting because someone claimed you? Or is their return rejecting? If their return rejected they will have to mail their return even if you amend. So they don't have to wait for you.
You should not amend until the first return has fully processed and you get the first refund or your tax due payment has cleared.
How to Amend this year
https://ttlc.intuit.com/turbotax-support/en-us/help-article/tax-return/amend-federal-tax-return-curr...
