Here’s a neat video on how to screen worm compost. Cassandra keeps it simple in this video and has some nice results. I do pretty much the same thing, except my screen is a repurposed basket with a piece of wire mesh placed in the bottom.
She makes mention of running a fan over the top of the castings when you first harvest them…it’s true- when you first remove your castings and put the worms back, the stuff is so gooey that a screen doesn’t work so well. Drying them out just a bit will help, although I wouldn’t want to dry them too much and risk losing some of their benefit.