Locate the spray holes. There might be one large hole at the very end of the boom or there might be several running down the boom's length.
Get out the nozzles that were included with the boom. Screw the nozzles or nozzle in tightly by twisting clockwise.
Make a test spray with the boom. If the coverage that you are getting with the spray is not wide enough, twist the nozzle tip or tips slightly counterclockwise to expand the coverage. If the coverage is too wide, twist the tips clockwise to tighten up the coverage area.