How do I brighten clock light it's very dim? - 2005 Buick Rendezvous

Is your clock part of radio assembly? There is usually a dimmer control for interior lamps, you rotate it to brighten or dim interior lamps--dome--instrument cluster--radio illumination. The same thing should work for the clock. If clock is part of radio assembly, I guess you can remove radio and dig into it, see if you find the wiring for clock illumination.