Unfortunately, you cannot file an extension after the deadline.
Keep in mind, if you
are getting a refund, you do not need to file an extension. You have three years from the tax deadline to file your return and claim a refund.
If you are not getting a refund, I recommend filing as soon as possible or at least making a payment to the IRS to minimize penalties and interest.
You can make a payment to the IRS
with a check or money order or you can pay
directly through the IRS Website here: https://www.irs.gov/payments.