There is nothing "special" you have to do to prepare your 2018 tax return that you have an extension for, except to make sure that the amount you paid to the IRS when you requested the extension is entered on your return.
When you requested your extension you were supposed to pay your estimated tax due. Did you enter the payment you made into your tax return? Go to Federal>Deductions and Credits>Estimates and Other Taxes Paid>Other Income Taxes
Otherwise, just prepare and e-file your 2018 tax return normally. You have until October 15. 2019 to e-file; after that you have to print, sign and mail it.
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**
