Root on A string
x133xx
B♭5 is the B♭ power chord. Its notes are B♭ and F. It is the same chord as A♯5. No third means no major or minor quality. Mute unused strings carefully.
x133xx
688xxx
Numbers show frets from the low E string to the high e string; x means don't play that string.
Every B♭ and F on the first 12 frets. The filled dots are the root, B♭. Build your own shape from any nearby group.
Other B♭ chords
Other power chords