Here is a good post, that is basically on jointing and honing to an already straight edge.
Hone a Straight Edge or to a Straight Edge?
The thread does get a bit side tracked about the interpretation of Iwasaki’s method, but there is still a lot of good discussion.
In that thread on post 33 there is a link to Alex Gilmore’s video of honing a razor. At about 6.25, Alex joints the razor using his interpretation of the Iwasaki method.
I believe in some of Glenn’s videos, he also demonstrates the technique as I describe below.
I typically just very lightly draw the razor from heel to toe across the upper vertical corner of the stone one time. It removes any false edge and straightens the edge. The bevels will no longer be meeting, but will come back to meeting in 6-10 light laps.
Alex says the technique is similar to killing an edge on a glass, but I feel a stone cuts a fresh edge, where a glass rolls the edge and it eventually breaks off.
Make sure to watch part 2, post 35, of Alex’s method.
BTW, Alex has many great videos of honing and his AX Method at his site, the Japan Stone.