How do you "ferment" crumbles?
The same way you ferment any chicken food. Add water. Same exact procedure for mash, crumbles, pellets, whole grains, grasses like dried alfalfa, etc...
There are tons of detailed guides and discussions on the topic, but if you want the extremely short version...
1. Container that is at least 3 times the volume of feed you want to ferment. This is because it is going to expand and fluff up when gasses are created.
2. Add some feed.
3. Add equal volume of water (same volume as the feed you added).
4. See how much water the feed soaks up, most likely going to happen within 30 minutes.
5. If feed soaks up all the water (it most likely will), stir it to see how wet or dry it is, and add more water until it is very soupy, bordering on "watery". Some people like to add enough water that there is a thin/clear water layer floating above food, but personally I just get it to a hot/freshly cooked "oatmeal" type consistency.
6. Wait 24-72 hours. You will know it is fermenting when you see it bubbling or you see little divots/air channels where gasses have escaped. Ever make pancakes? Know how you know it is time to flip them when you see the bubbles popping? Same sort of thing to look for in fermented feed to know it is working. Also, it will most likely smell a little like sourdough bread, or a little tangy/acidic if you take a whif.