Contact TurboTax support and speak with an agent as they may be able to push Windows installation files to your download account at no charge. Note the TurboTax only supports prior tax years of 2016 thru 2018.
Support is open from 5am to 5pm Pacific time, Monday thru Friday
Use this website to contact TurboTax support during business hours - https://support.turbotax.intuit.com/contact/
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Call in and ask them to push you the Windows downloads. But they probably only will go back 3 years to 2016.
You need to move the .tax2018 file from Mac to transfer into 2019. Both the Mac and Windows versions use the same .tax data file. So you don't need to convert it. I would copy all the .tax files and pdf files from the Mac to a flash drive, then copy them to the PC. They should go in your Documents then under a Turbo Tax subfolder.
Also if you haven't done it, I would open each year in the program and save it as a PDF file, go to File-Save to PDF so you don't need the program installed to view or print your return in the future like to get a mortgage or loan, etc.