Transpose -1 Semitone ⌥↓ – Logic Pro keyboard command of the day

  Transpose –1 Semitone ⌥↓

Transpose the selected step down  half-step. A semitone is one twelfth of an octave.

Edit Step Sequencer steps in Logic Pro – Apple Support

To transpose the pattern down one semitone: Choose Transpose –1 Semitone.