Phono setting and MC/MM

I have some doubts about it, in the past maybe only the big vintage receivers top accepted MC cartridges in the connection, usually they were only predisposed for Cartridges MM.
What receiver is it, do you have brand and model by chance?

If it’s a high output MC there is no problem! What cartridge is it?

Tell him to try, if it’s too quiet with LOMC then it’s MM phono stage.
If it’s MM phono stage he could add a SUT (or headamp) and it will be fine to LOMC cart.

I strongly doubt the receiver is switchable to MC.  He will probably need a separate "head amp" (phono pre-preamp).  I would guess old head amps are available used for $50-$100.

Probably an older Mac, they would do MM, MC or MI. 3.5mv or better would work, load the MC cart correctly and away you go.
No your receiver is a MM cart.

The MC cart you have unless it's like a 5mv or higher. High output MC 

Look up the model number on the cart and see what the specs are. Google works great OP without a name and model. They are all different..