If you have not filed:
You can use clear and start over to begin again. See the FAQ below. Using Clear & Start Over in Turbo Tax Online
If you have filed:
You'll need to wait. After you click Transmit Returns Now, your e-file goes to pending status, where it will stay until it's either been accepted or rejected by the government.
Think of pending as "in transit" or "in limbo" – just like you can't cancel a letter that you sent yesterday, you can't cancel a return that's on its way to the government.
