How can I start over my taxes ? I haven’t submitted anything yet .

You can start your tax return over by using our clear and start over feature in TurboTax Online as long has you haven't submitted payment, deducted the TurboTax fee from your refund, or registered, please see this TurboTax FAQ for more information:

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

And what if it dont let you star over

If you already submitted then you can't start over. If you haven't submitted it you can use this FAQ to clear and start over.

Uninstall TurboTax and reinstall it again and start importing/entering your information.