A dim7/D#
The A dim7 chord consists of the A (Perfect unison), C (Minor third), D# (Diminished fifth) and F# (Major sixth) notes, with D# as the bass note.

How to play the A dim7/D# chord
- Play D# as the lowest bass note in the left hand
- Find A (Root) on the piano keyboard
- Add C (Minor third) — 3 semitones above A
- Add D# (Diminished fifth) — 6 semitones above A
- Add F# (Major sixth) — 9 semitones above A
- Press all 5 notes simultaneously to sound the A dim7/D# chord