I'm a little unclear on specifically what you're asking about, which lever and how is it moving currently?

I've got a similar mag trainer at home, Minoura or Cyclops maybe?, and is has a screw/knob to position the spinning hub in or out to adjust friction against the tire, then mine also has a small lever that rotates or slides (depending upon how you define things) to adjust the amount of resistence in the mag unit.

Plus the pic is a bit fuzzy.