For RTB prefs your gamemode would need a server.cs file.
Here's an example from my score saver.
if(isfile("Add-Ons/System_ReturnToBlockland/server.cs"))
{
if(!$RTB::RTBR_ServerControl_Hook)
exec("Add-Ons/System_ReturnToBlockland/hooks/serverControl.cs");
RTB_registerPref("Toggle","Score Saver","ScoreSaver::Toggle","bool","Server_ScoreSaver",1,0,1);
RTB_registerPref("Can Reset Scores","Score Saver","ScoreSaver::CanReset","list Host 1 SuperAdmin 2 Admin 3","Server_ScoreSaver",2,0,1);
}
else
{
$ScoreSaver::Toggle = 1;
$ScoreSaver::CanReset = 2;
}
Once you've done all that go into your gamemode.txt and type in ADDON Gamemode_GamemodeNameHere and save.