The remote.xml files for the Fire TV Stick that you are linking to will not work on OSMC unfortunately - they are designed for use on a Fire TV Stick running Android.
This because a Fire TV Stick remote on an Android device acts as though it is a keyboard device (generates keyboard scan codes) while on OSMC it acts as a remote control, thus the remote.xml needs to be modified.
Does the remote work at all for you ? The remote.xml only changes the mapping of the buttons to be a bit more useful but isn’t required for it to work.
You could try downloading the remote.xml that I rewrote for OSMC for the Fire TV Stick remote here: