They have one now that looks completely normal too, not their hideous old remote

If your fireplace has a fan then you have power there.

With the model of the fireplace or the module inside, we could tell you in greater detail how it can be switched.

They basically all support a thermostat in addition to a manual switch. Thermostats are frequently in the form of a remote control, with a module that’s just plugged in to spade terminals beneath the fireplace. For a dry contact style fireplace the module is battery operated.