Basically by honing something steel other than razors. I think a lot of guys use chisels or something, but I used the backside of a kitchen knife I didn't care about. Essentially just trying to hone the backside of the knife. It will smooth out the surface of the diamond plate as you hone. You just need something steel that you can try to hone, and that will break it in. You could also try lapping some waterstones to break it in, although I wouldn't try this on one of the finer plates like the 1200 grit (E) or 8000 grit (EE).
The way the DMT plates come, the initial surface is too harsh for honing razors, but as you use it, it will settle in to being a nicer, smoother surface.