To install a humbucker cover, you need to have a cover that fits your pickup. The cover should fit snugly but shouldn’t be forced over the pickup.
Installing the cover is simple. Add double-sided tape to the pickup (while ensuring it doesn’t cover the screw coils) and place the cover on the pickup. Although you could leave it like that, it’s a good idea to solder the cover to the baseplate near the center of one of the long sides of the pickup.
Don’t keep the soldering iron near the pickups for long, as heat can damage the humbucker.