AQ You can't file an extension after April 15th.
However, if you e-filed your returns by the April 15th deadline, you have a five day grace period to get them fixed and resent by e-file or mail. You have until April 20th to fix and resend your returns.
For more details, check out the TurboTax FAQ below:
https://ttlc.intuit.com/questions/2562196-what-if-i-e-filed-before-april-15-but-my-return-got-reject...