You will need to wait for your original tax return to be accepted by the IRS. Once that has occurred then you can amend your tax return.
To amend your return you need to log into your TurboTax account to see an option to Amend a Filed and Accepted Return. Click on that to start the amending process. Once you are finished making changes to your return you will need to print it out, sign, date and mail it to the IRS.
Please see the below FAQ for more information on amending your tax return:
https://ttlc.intuit.com/community/amending/help/how-do-i-amend-my-turbotax-online-return/00/27577