Is this a 3-piece crank with square-taper loose-ball BB? Remove left-side crankarm. Loosen lock-ring. Tighten adjustable cup. Tighten lockring. On certain cranksets with long BB-spindle, you can even make the adjustment without removing the crarnkarm.
but its a sealed bearing BB shell and the cranks are race face ride cranks with that hollow axel if you know which ones i mean
and its the drive side BB that moves
that bike nut
Unless they are just loose, usually when a cartridge unit develops play it needs to be replaced.