Here is a great FAQ from Microsoft on transferring files to an external hard drive.
Thanks but will doing this allow me to still use these older Turbotax applications(2013-2018) , if needed?
It's not guaranteed. TurboTax only provides updates and support for the current year's tax software, plus three years prior. So for this year, TurboTax software for 2016, 2017, 2018 and 2019 should work fine. Anything prior to 2016 may not function properly.
Reference: Can I use TurboTax to prepare 2015, 2014, or earlier tax ...
Ok ... first you can only move FILES to an external hard drive NOT the programming. If you need to use the programming later it will need to be on the computer already or it will need to be reinstalled. Then to work on any returns the FILE must be returned to the computer's hard drive to be opened by the program ... it will not work off the external hard drive directly.