Not quite sure what you are asking. If you needed to request an extension for a 2018 tax return you had to make that request by April 15, 2019. That extension gives you until October 15, 2019 to prepare and file your 2018 return. The extension only gives you more time to prepare the return--not extra time to pay your tax due. You were supposed to pay your estimated tax due on or before April 15, 2019.
You can e-file your 2018 return until October 15, 2019. After that, e-filing will close and the return would have to be printed, signed and mailed.
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