If you qualify as his dependent you need to amend your return. But he will have to print and mail his return even if you amend. So he doesn't have to wait. He should mail it right away.
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...
