BOL BPM Blank Title 106256

I'm looking for some help with the Bill of Lading Module. I added 4 fields to the line tab. I would like to be able to type the packing slip and line number into two of these fields and have it pull the part information for that particular line on the packing slip. Anyone know of a way that I could accomplish this? I have tried some stuff with BPM's but cant seem to get it working correctly.