For what year? Did you use the Online version?
You can amend the current 2019 return online.
For 2018 and prior you have to install the Desktop program either from a CD or download. Turbo Tax has special Amend programs you can download. Actually you might've able to amend 2018 online now too.
How to amend
https://ttlc.intuit.com/community/amending/help/how-to-amend-change-or-correct-a-return-you-already-...
