7.1 and no it doesn't find it on play store
Was your S7 purchased recently? I think S7 models on the shelf just now are factory loaded with Android 7.1 which is why you may be having issues. As I said, I'm using Nougat 7.0 which is the most recent software I can get OTA and having no problems.
Your only option really is to downgrade from 7.1 to 7.0 in order to allow compatibility with LibreLink. There is a bit of a knack to this process however, as it does involve being able to use software such as ODIN, booting your phone into various modes, and downloading the correct USB drivers and ROM for your desired firmware.
If it's something that you're not confident in doing, then you could always check in with your local mobile phone repair shop, O2 store, EE store, etc. They might be able to do it for you.
Your other option is to wait for LibreLink to cater for the newer software if possible. But that has the potential to be a very long time...