C m9/Gb
The C m9 chord consists of the C (Perfect unison), Eb (Minor third), G (Perfect fifth), Bb (Minor seventh) and D (Major ninth) notes, with Gb as the bass note.

How to play the C m9/Gb chord
- Play Gb as the lowest bass note in the left hand
- Find C (Root) on the piano keyboard
- Add Eb (Minor third) — 3 semitones above C
- Add G (Perfect fifth) — 7 semitones above C
- Add Bb (Minor seventh) — 10 semitones above C
- Add D (Major ninth) — 14 semitones above C
- Press all 6 notes simultaneously to sound the C m9/Gb chord