The best way to do that would be create a switch on the master page and turn off ALL the channels for all fixtures except those with a dimmer function. then once your switch is created, click on it then go to buttons> settings> dimmer/ speed, then look for a "show a fader into the button section and check the dot next to "Show the dimmer fader" ok? Let me know if you need help doing any of this.
Sincerely,