Multiple switches, Vent fan

I'm afraid I haven't the vocabulary to do a google search on my own. Here's what I'm doing, and what I need an answer to:
Replacing a bathroom vent fan with a heat lamp. Original brand is unknown. I have a 3 switch wall plate. One to a separate track light, one to the fan and a third to the heat lamp. I assume anything I buy with be plug and play but all inclusive of a single switch. The one I'm probably going to buy has a single mutli function switch (Light/Nightlight/Fan/Bluetooth Speaker)
So, what to do with the third switch?
Can I pop an a/c outlet into it's place? Do I leave the original switch in its place? Then what happens with those wires at the unit? or at the switch? Can I ground it somehow and put a blank plate over it?
You can see how google is no help ;-)
Hope I've come to the right place.
Thanks for the look,
Best regards

 

Cap the unused wire at the new fan.
Leave the switch and let people go nuts trying to figure out what it does.
You may not be to put a receptacle in place of the switch depending on the cables in the switch box

 

Thx Much. Should be an easy day, if I don't zap myself ;-)

 

It is possible (depending on the age of the installation) that you have Despard devices you can still find parts for it either on eBay or the link I left to Kyle Switch Plates.