If you have already filed, you cannot just return to the program to delete, unfortunately. You have to wait until your return is either rejected or approved.
If it's rejected, you can return to the program to remove the information while fixing the error.
If your return is approved, you would need to amend if removing the 1099-G changes your original refund amount or tax due. To amend, please click here 2018 Amend. Follow the instructions in the program and it will tell you if the correction changes the result. If you do need to amend, please wait until your return is fully processed and you have received your refund or your payment has cleared.