Profurl roller main halyard replacement

[reelife]

I have an older attached profurl roller main system on my Van 32 .Recently notice on my last trip up the mast the halyard was in need of replacing near the top. I spliced a new loop on the other end of the halyard and I thought I could just lower the sail, unhook the halyard, put on a tacer line then attach a new halyard. The end of the halyard doesn't come out at the bottom? Its within the furling aluminum cover. How the heck do you replace the halyard??
Geordie -Providence II