Guitar chords in the key of F:
F Gm Am Bb C Dm Edim

Chord Fmaj7b5 notes: F, A, Cb and E. (Cb=B).

You must leave out the 6th and 5th strings.

The guitar strings 2(Cb) and 1(E) are left open.

F major 7 b5 guitar chord's alternative names: Fmaj7b5, Fmaj7(b5).

Steps: 1-3-b5-7.
1(F), 3(A), b5(B/Cb), 7(E).