You would need to access your 2018 return and go through the pdf to find that worksheet (Alternative Minimum Tax) and then scroll down to the line you want.
https://ttlc.intuit.com/community/prior-year-return/help/how-do-i-access-my-prior-year-return/00/27010/message-id/746
You can get a free transcript from the IRS:
https://www.irs.gov/individuals/get-transcript
How do I get a copy of a return I prepared using desktop TurboTax?
https://ttlc.intuit.com/questions/1900639