I had the same problem with my previous Bav34. My solution was to remove the end fitting off the boom (just enough to see into the hollow section). I taped a small rightangled offset screwdriver on to the end of my extended boat hook and with my arm inside the boom slowly “clawed” the free end of the reefing line back to the pulley the full length of the boom. Also needed a torch sited inside the boom.
Like fishing , it requires patience but the prize is worth the effort and you know it wont happen a second time.
Good fishing !!!