The suction valve is the 3-way valve that controls the pool to spa suction and is on the suction line right before the pump inlet (lower actuated valve). You want that handle pointing to the left. The toggle switch on the bottom of the actuator can move the valve for you by move the switch to the opposite side. Once done, move the switch back.
But I just noticed that the return valve (higher actuated valve) appears to be in the middle of pool and spa so some water is always going back to the spa. You will need to put the actuator toggle in the middle position and manually move the valve to shut off the spa (handle to the right). Once done, move the valve handle back where it was and the toggle switch back where it was.
But if you have never done this before, perhaps you should use Matt's suggestion.