If there’s no hole in the centre of the post to poke the string end down, then looking at pics of other IB bass kit builds, people often seem to put the first wrap above the string end going through the slot and the rest then below the string end.

I must admit it’s not a great tuner post design. The bottom of the slot is at the base of the curved section of the post, and not in the centre, so the tendency is for the string wraps to push the string up the post.