Not sure if you still need help with this but Redshift/RoyalRender user here for the past 6 years or so. Setting this up is a bit confusing but you're on the right track.
In your local preferences folder (c:\Users\you\AppData\Roaming\MAXON\Cinema_Version) you'll find a settings.userinstallation.json file. This stores the path of the shared asset database that you set up to use locally.
The next step is to copy that .json file to a shared location and edit the Royal Render environment to use that shared prefs location. The RR docs explain how to edit your environment variables but again it can be a little confusing with all of the files involved.
In the RR install folder the environment files are in //RoyalRender/render_apps/_setenv/all. There is an environment config for each 3D app so look for the cinema 4d*.rrEnv ones. Note that the only one you should create/edit is the cinema 4d__inhouse.rrenv file. This is your custom environment that remains untouched by any RR updates. Add the g_userprefs = Z:\PATH_TO_SHARED_PREFS line to this file. All Royal Render clients will now use that shared prefs directory and the corresponding asset database(s) that are defined in the .json file.
JSoft's post in Asset Browser and Royal Render was marked as the answer