A B♭ Major (B♭) chord contains the notes A#, F, D. It is built from the major formula 1 - 3 - 5, with Bb as the root.
Is B♭ the same chord as A♯?
Yes — identical pitches, identical fingering, different name. Which spelling is correct depends on the key you're in: D minor has one flat (B♭), so B♭ is the right name there. You'd only call it A♯ in a sharp key that needed it.