@ extreme P
He was not asking about the STAB TRIM CUTOUT switches, but about the STAB TRIM OVERRIDE switch. This one is located at the aft of the center console.
Normally electric trim operation is interrupted if you apply elevator force in the other direction. There are control column actuated stabilizer trim cutout switches for this.
By switching the stab trim override switch to override, you will override this system and electric trimming is possible while applying elevator force in the opposite direction.
I can immagine using this when there is a problem with the cutout switches, however there is no reference to this switch in the QRH so maybee it is only used by maintenance.