Of course, firstly you have to find them in the shed. Look for white powdery dust on the perches, at wall joints and under feeders, nestboxes and water containers. These are the mites' poop. Take a look in the shed at night using a flashlight. On white birds, they stand out very clearly.
Eradication is a two stage process.
Firstly, you need to protect the birds from the insects at night and secondly, the bugs have to be killed in their hideaway homes. The good old malathion bath is the best thing to protect the birds. Remove all nests, food containers and waterers from the shed, clean out the old litter and preferably burn it. Scrape any hard manure off perches and floors as mites love to hide underneath such stuff. Liberally paint kerosene on all perches, floors and along cracks and wall joints.