AFAIK, micro greens are just regular greens that you plant really close together and then harvest before they get mature.

Please someone correct me if this isn’t technically microgreens but what I’ve done in the past to get mini salad greens is you just get one of those larger seedlings trays (or you can use old milk cartons cut in half), put some soil in it, and plant seeds in really dense rows (like >10 seeds an inch). Then you just harvest them when they get to be an inch tall or something similar. I just use regular collard, kale, mustard, and lettuce seeds from the garden shop.

You can also grow stuff from the grocery store. One of my favorites to grow is pea shoots. You literally buy a bag of dried peas from the grocery store and plant them like I described above. Then harvest them when they get about 3-4 inches tall. They go great in spring salads. Mung beans are another grocery store staple that I love sprouting on my own instead of buying the sprouts.

Not sure what your kit looks like but you can definitely grow micro greens in potting soil as well if you run out of whatever the kit has! Just make sure you’re keeping an eye on moisture so they don’t stay too wet or get too dry. Because micro greens are basically seedlings, you don’t actually need to fertilize them at all and they can actually grow in pretty spare soil.