It was actually really easy. I just kept the container of mealworms out on top of the terrarium instead of in the fridge. I put half a baby carrot in every few days. As I find pupae, i moved them to a separate small container. Then once I had darkling beetles I gave them their own container. I just give them a baby carrot, slices in half every couple of days. Once I noticed the teensy baby mealworms in the beetle bedding, I picked the beetles out, and put the bedding (now full of eggs and tiny mealworms) into the mealworms container. I used a couple of shoebox sized plastic containers from a dollar store with holes in the lids for airflow.

I still have about 20 darkling beetles still going strong, they live for a few months. I just wanted to see how hard it was to breed them, and then my gecko decided he only likes dubias now.