Help with Replacing Rheostat on Heat Exchanger Blower Box

[Jmuduke]

Hello All - my friend’s kid accidentally broke off the rheostat knob on top of this blower box for this fireplace heat exchanger. I was hoping to replace it but can’t figure out how to open the box. Alternatively, are there separate blower boxes for sale that would work as a replacement?

Thanks in advance for your time and assistance!

 

[begreen]

Was the rheostat's shaft broken when this happened? If it's still intact then a new knob can be purchased.
We need more views of the other side and bottom to see if there is a way to service this.

 

[Jmuduke]

Was the rheostat's shaft broken when this happened? If it's still intact then a new knob can be purchased.
We need more views of the other side and bottom to see if there is a way to service this.

I’d say about 25% of the rheostat’s shaft is still intact so don’t think I can just place a new knob on top. The other side looks identical to the side shown and the bottom just has 4 rubber “feet” for it to stand on. Happy to still post photos if still helpful however? Someone else said to drill out the rivets but was hoping to avoid that

 

[begreen]

It may take drilling out the rivets if there are no other fastners. If so, that's not that big of a deal.