It is just a dust cover to keep it clean and dry. You can leave the piston side on the piston and pull the other side of the caliper, straighten it and pop it back on. Add a little grease to make it easier to put back on.
Pull the boot off the piston end, untwist it, and roll it back on the piston. You will most likely have to use a pick, or a dentist tool to get it off the piston.