If you have already filed your taxes, you won't be able to cancel your return. If your return has been accepted, you will need to file an amended return to add the information you need to change.You should not try to amend your return until the original return it has been fully processed and you have received your refund or your payment has cleared. 

If your return is rejected, you are able to go back into your return and make the changes needed, then e-file the return again without doing the amendment.

If you wanted to delete your tax return, read here - https://ttlc.intuit.com/questions/1899886-can-i-delete-my-tax-return-in-turbotax-online

Please see the instructions below to amend a return:

 https://ttlc.intuit.com/replies/3288565