I don't believe there is a switch. You change jumpers to use either MM or MC. They should be clearly marked on the board. There should be another jumper that changes gain +-
Narrod is correct. I purchased a Unico SE in March and made the MC change in its phono board for my Denon 103 D cartridge (Rega P2 table). There are very faint MM and MC markings on the circuit board, way back on the LHS as you look at the from of the amp. I also changed the gain 10db, only to find out that the output from the phono section was too high. I returned the 10db jumpers to the factory position and everything works just fine now.