F# 6/C#
The F# 6 chord consists of the F# (Perfect unison), A# (Major third), C# (Perfect fifth) and D# (Major sixth) notes, with C# as the bass note.

How to play the F# 6/C# chord
- Play C# as the lowest bass note in the left hand
- Find F# (Root) on the piano keyboard
- Add A# (Major third) — 4 semitones above F#
- Add C# (Perfect fifth) — 7 semitones above F#
- Add D# (Major sixth) — 9 semitones above F#
- Press all 5 notes simultaneously to sound the F# 6/C# chord