Those are my favourite type of reels.

First you need to cut off any leader.

Then just insert the end of the film fully into the centre core area, under the strut two away from the hooks (actually guides) and over top of the strut that is adjacent to the hooks/guides. Essentially, you crimp the film on that adjacent strut, and roll it in to the spiral, going over top of the hooks/guides.

It is much easier to do or show this than it is to describe it.