You can delete the amended return this way. Do the steps slowly and carefully. After you delete it then you need to manually take out the changes you made to put your return back to the original return.
How to delete an Amended return in the Online version
https://ttlc.intuit.com/community/amending/help/how-do-i-cancel-or-undo-an-amended-return-in-turbota...
Were you trying to change your original from mailing to efile?
How to change from Mail to Efile in the Online version
https://ttlc.intuit.com/community/e-file/help/how-do-i-change-from-mail-to-e-file-in-turbotax-online...
Click on Add a State to let you back into your retun.
