I am on the page where it says that i have filled my 2019 taxes and they are ready to mail, i want to delete and start again, how do i do it?

https://ttlc.intuit.com/community/using-turbotax/help/how-do-i-clear-and-start-over-in-turbotax-online/00/26444

As long as you haven't submitted payment, deducted the TurboTax fee from your refund, or registered, you can erase your return and start from scratch in TurboTax Online.

1. Sign in and select a topic to continue your return.
2. On the next screen, from the left-side menu, select Tax Tools, and then Clear & Start Over (select the menu icon in the upper-left corner if you don't see this menu).

If you have already paid or registered you will not be able to use this feature.  In this case you would only be able to edit your return or create a new account.  You can switch to e-file without starting over by clicking on the File tab in the left menu and changing your option from File by Mail to E-file.