Every fingering that fits a hand
323x
easy · no 5
3231
moderate · no 5
3535
moderate · barre
xaaa
moderate · barre · no 5
3235
hard · no 5
What is true of it
B♭6 is B♭, D, F and G — 1, 3, 5 and 6 counted from B♭.
These are also the notes of Gm7/B♭. Which name is right depends on what is underneath and what came before — the notes alone do not decide.
On an instrument that cannot reach all 4, the 5 goes first, in that order.
The easiest of the 5 fingerings below is 323x: 3 fingers, held at the 2nd fret.
None of them uses an open string, so this chord moves up the neck unchanged — the same shape 1 fret higher is the chord a semitone above.
2 of the 5 need a barre.
It leaves out the 5. 4 strings cannot carry 4 notes, and the 5 is the one this chord can lose without changing what it is.
1 string stays silent.
Where its notes are on the neck
The brass dots are B♭, the root. Everything else is a chord tone with its degree printed in it.
With a different note underneath
B♭6/D
x231
B♭6/F
aaaa
B♭6/G
0211
An inversion is the same chord with a different note lowest. The name changes to a slash name because the bass is what a listener hears as the foundation.