On the S7 I would expect TWRP Recovery to be installed already – but don’t install the TWRP app, it is a different thing and can have downsides.
Power the phone off, then you can check by using the hardware buttons to boot into Recovery
With the device powered off - hold Volume Up + Home + Power. When the blue text appears, release the buttons.
You might read a bit of these articles first.
Please check the section Reboot in second article, so that you know how to get out of recovery !
Edit, once you have got your bearings (and please be prepared to spend a little time doing this) – my method involved navigating to Advanced > File manager.