go to server/gameserver/config/altsettings file open and find these lines:
# Allow use Event Manager for change occupation
# If you need change occupation only use quest then set this to False
# (1,2,3 = 1st, 2nd and 3rd classchange)
# Default = False
SpawnClassMaster = True
AllowClassMaster1 = True
AllowClassMaster2 = True
AllowClassMaster3 = True
set to true like the above and the class manager will spawn and your players will be able to change all 3 classes from him if you want only 1/2/3 class just set to false