To be honest I am not sure if you just want to waste the time of the developers or you really want to bring value to OSMC (that you love so much).
If you want to test Netflix and Amazon on OSMC by using a alpha/test version of Kodi, which is exactly the same as the method described in the article (which is behind a paywall) for libreelec (actually articel points to this forum entry https://forum.kodi.tv/showthread.php?tid=298461) you just follow the simple steps installing OSMC and follow the steps described and shared to you here
[TESTING] Kodi 18 (Leia) builds for Raspberry Pi - #352 by gmc
As simple as that follow the steps and then follow the thread to work with the developers to fix issues that may exists in that version.