If you have not filed your return you can get back in by:

1. Sign into your Turbo Tax account

2. Click on tax home or take me to my return

3. Scroll down till you see Your tax returns and documents

4. Click on your 2018 return, and then select add a state (you are not actually adding a state, this just prompts the correct menu)

5. Navigate to where you need to on the return

If you already filed your return you will need to wait to see if it was rejected or accepted. If they were rejected you are able to login to your return to fix what you need to fix and fix the errors that caused the rejection and refile the return. If your returns were accepted, then you will need to file an amended return. 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.
Amended returns do not “catch up” to your original return and replace them; they are processed as two separate returns.  
Amended returns have to be printed and filed by mail.  It can take the IRS up to 12 weeks or longer to process them.   If you are due a larger refund than on your original return, your amended return should only show the difference and you will receive a separate check for it.  If you owe money on your amended return, it will show only the new amount owed, you will have to mail a check with the return. You can check the status of your amended return by clicking here: https://www.irs.gov/filing/individuals/amended-returns-form-1040-x-/wheres-my-amended-return-1

 Click here for amending instructions: https://ttlc.intuit.com/replies/3288565