Sounds like a lever – probably from the late 70’s?
There should be a short edge, and a longer lever end, with the cntrol lines attached to this end.
The short edge is connected “in line” between the bottom of the king post and the boom. Then, when you pull down on the long end, the boom is pulled down by the twist in the short end.
The long end may need a piece of elastic to hold it into the triangle of kicker / boom / mast: that way it is out of the way of the crew.
Getting the correct length for the short end (so you can let t off, and yet still use the lever to pull it in) is very tricky. In the late 70’s we used all sorts of clever gadgets on the bom to achieve this! Switching to a cascade system can end up being much easier.