C# m7/A#
The C# m7 chord consists of the C# (Perfect unison), E (Minor third), G# (Perfect fifth) and B (Minor seventh) notes, with A# as the bass note.

How to play the C# m7/A# chord
- Play A# as the lowest bass note in the left hand
- Find C# (Root) on the piano keyboard
- Add E (Minor third) — 3 semitones above C#
- Add G# (Perfect fifth) — 7 semitones above C#
- Add B (Minor seventh) — 10 semitones above C#
- Press all 5 notes simultaneously to sound the C# m7/A# chord