Your FLkey 2 keyboard gives you both Octave and Transposition options.
When you power on your FLkey 37 its keyboard defaults to the note range C2 -C5 where C3 is middle C.
You can change the octave range using the Octave - and Octave + buttons. The octave shift range for the FLkey 37 is -4 to +4 octaves.
To reset to the default octave, press both Octave - and Octave + buttons together.
When you change the Octave range, the screen temporarily shows the octave shift in a number (e.g +1) and the range the current keyboard is at, e.g. C1 – C5.
In addition to the temporary screen display, the Octave buttons light to show the octave position.
With no octave shift, the Octave buttons are dim. When you shift up an octave the Octave + button lights brighter, when you shift down an octave the Octave - button lights brighter. The button brightness shows the shift amount, the brighter the button, the more the shift.
In total, there are 128 MIDI notes. 128 is not divisible by 12 so you can shift the octave and transposition, so some keys are out of the MIDI note range. When you shift to the extreme ends of the MIDI note range, out of range keys won't play any notes.
You can transpose your FLkey 2 37's keys up or down in semitone increments. The transposition range is ±12 semitones.
To transpose the keys, hold the Shift button and press Octave - or Octave +. Octave - transposes the keys down one semitone, Octave + transposes the keys up one semitone.
To reset to the default transposition, hold Shift and press both Octave - and Octave + buttons together.
When you change transposition, the screen temporarily shows the semitone shift as a number and the current keyboard range.