I'm linking you to the TurboTax Help Article that explains in detail how to amend your 2018 return.
Keep in mind that amended returns cannot be e-filed. They must be printed and mailed.
https://ttlc.intuit.com/community/amending/help/how-do-i-amend-my-turbotax-online-return/01/27577
*** I am NOT a tax expert. I am a seasoned TurboTax user, and volunteer to provide assistance to TT users. Nothing I post is to be considered TAX ADVICE; I bear no legal liability for responses.***
