You need to provide more detail, but if it matches the picture on your profile, you have an end piece for an adjustable outhaul. You will need to use a new piece of line with a knot in the end of it, if you aren't going to use an adjustable setup.
Can anyone tell Me where to find a schematic on how to rig a an older Chinook boom?
One of these?
chinooksailing.com/pages/support#boom