Guitar chords in the key of A# or Bb:
Bb Cm Dm Eb F Gm Adim

Chord Bb9-5 notes: Bb, D, Ab, C and Fb. (Fb=E).

You should not play the 6th string.

The guitar strings 4(D) and 1(Fb) are left open.

Bb(A#) dominant 9th b5 guitar chord's alternative names: Bb7(b5,9), Bb9b5.

Steps: 1-3-b5-b7-9.
1(A#/Bb), 3(D), b5(E/Fb), b7(G#/Ab), 9(C).