For replacing a drill chuck, first of all, turn off your drill and unplug it. Then you need to remove the chuck key and the chuck jaws. Next, you need to unscrew the retaining nut and you’ll be able to easily take out the chuck.
After that, you’ll be able to open the jaws of the chuck and you’ll see the chuck key. Then, remove it carefully and you’ll be able to take out the chuck. Then, you’ll be able to put the chuck key into the new chuck and then you’ll need to put the new chuck into the drill.