Worm chow is just dry ingredients you can feed to your worms to fatten them up or for supplementing nutrients to make sure they are being fed well! If you just want to fatten them up short term for fishing you don’t have to get too fancy with it, but if you are caring about the quality of your castings it can be beneficial!
I get asked a lot, so here is a link to my worm chow guide and recipe if you are interested! I also sell it on my website if you don’t want to make it yourself.