How to Access Old App Versions

[gw1500se]

I have acquired an iPhone 5 (IOS 10.3.4) and want to install an app whose current version requires IOS 11. I have read various articles on how to get old versions of apps that are compatible but none work. It seems the key to getting old apps was to work through iTunes and the app store. However, that is not longer possible with the current version of iTunes. Is there still a way to access and install old versions of apps that are compatible with my IOS? TIA.

 

[gw1500se]

I figured out part of this. I needed to download an old version of iTunes that still had access to the app store. However, I can get the app in iTunes but since it is a free app I cannot figure out how to 'purchase' it. According to my research, once I 'purchase the new version I can then install it on the iPhone and it will automagically get the older version. So the question is, how do I 'purchase' a free app or somehow get it into iTunes on my PC?