If you mean how to thread the lines through the boom, I used an electrical fish tape you can buy from any big box store, Harbor Freight, etc. Push it through the boom around the sheaves and then attach a small diameter messenger line to the end of the tape (try to pull the tape's end through the other end sheave). Then pull each actual line (outhaul, reefing, topping lift) using the messengers.
I rigged my topping lift a bit differently so it would be easier to remove the boom and to adjust it. Instead of having a line run from the front of the boom, through it, out the aft end and then all the way up to the mast crane, I did this: attach a fixed line (wire rope or line, your choice) to the mast crane (I used wire rope as it was already in place when I bought mine). Make that line long enough to reach to about 3 ft above the end of the boom when the boom is level. Attach a small swivel block to the end of that line/wire. Run your topping lift line (could be like 1/4 in diam) through the boom, out a back end sheave, up to and through the block, then down to be tied off to the fitting at the end of the boom (or use a bowline and small shackle if you prefer). It is easier to adjust the height that way, and you do not have to remove the line through the boom when you haul the boat - that line always stays inside the boom, and is just untied (or unshackled) and pulled out of the swivel block to remove and stow the boom.