I got an email stating I need to enter my 2018 AGI, but I can't find where to input it? I've looked at other questions as well, but can't find the "file" tab

Here is where you can find the file tab in TurboTax:

1. While in your Tax Home (open the Personal Info Module),

 

    2.  Select File from your left side menu:

 

 

    3.  Follow the on-screen prompts to get to your 2018 AGI.