Are you really looking for your 2018 refund amount or do you want to e-file your 2019 return? If you are trying to e-file your 2019 return you need your 2018 AGI from line 7 of your 2018 return, not your refund amount.
If you do want your 2018 refund amount look at your 2018 return on line 20a
https://ttlc.intuit.com/community/prior-year-return/help/how-do-i-access-my-prior-year-return/00/270...
You can get a free transcript from the IRS:
https://www.irs.gov/individuals/get-transcript
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**