The speed brake has no settings like a switch or a knob, it is a handle lever that works vía xplane speed brake axis dataref
To control the speed brakes lever, you may:
A. you can map xplane speed brake axis to a hardware handle lever you have (same as you map a throttle lever)
B. you can map 2 buttons or keys to xplane 'sim/flight_controls/speedbrakes extend one' & 'speedbrakes retract one' (each clic will cycle them up or down a bit)
C. you can make a lua script or similar to manipulate xplane dataref speed brakes axis writting values 0.xxxx to 1.0 (sim/cockpit2/controls/speedbrake_ratio)
Or did you mean wheel brakes knob settings? (RTO, OFF, 1, 2, 3, MAX)
dataref 'ixeg/733/hydraulics/hyd_auto_brake_act'
RTO = -1
OFF = 0
1,2,3 setting = 1,2,3 respectively
MAX = 4
hope this helps