You will not be able to clear and start over but you will be able to make the necessary changes that you need to fix.

yes , you can , but if you need to do changes , do it as 1040ex or amendment return and justified your changes , don't do it like new, just make like amendment 1040Ex

Ignore that answer by emisal.  You only do an Amended 1040X return if your original return was accepted.

Sorry you can't start over.  Unless you haven't paid any fees yet.  Then you could start over by setting up a new online account.  You will have to go back through and manually change it.