What year are you needing to amend?
2019 won't be available till late February around the 26th, that date is subject to change. Also, you will need to mail in an amended return.
Please review the following article for more information.
How do I amend my 2019 TurboTax Online return? - Community
For years 2018 or earlier, please use this link: https://ttlc.intuit.com/community/amending/help/how-do-i-amend-a-return-in-turbotax/00/27579