It appears IRS did not get my 1098 from one of my mortgage companies and I missed some capital gains dividends on my 2018 return. I would like to upload my 2018 return and fix it to see what the return would say I owe, or should get back. Is it possible? If so, can you be specific in where exactly I go on this website to do that as I don't know my way around the site very well. Thanks!
There is no way at all to work on a 2018 return online. And you say you used desktop software to prepare that return, Did you uninstall the software and throw away the CD? (Why?)
If you need to amend that return it must be done using 2018 desktop software. Do you have the tax file saved in your hard drive? Returns prepared using desktop (CD/download) software are not stored online--they are only stored on your own hard drive.
See if customer support will provide a download of the 2018 software for you so that you can amend.
To call TurboTax customer support
https://ttlc.intuit.com/questions/1899263-what-is-the-turbotax-phone-number
They are available from 5 a.m. to 5 p.m. Monday - Friday Pacific time.