How much play is there? If it's only a little, I wouldn't worry about it at all. If it's really bad, send it in. Not too much, maybe you can do it yourself.
To remove it, you need to move the bolsters closer to each other. I've found the best way to use a vise not a hammer, it's a little more precise imo. Pad the jaws with two blocks of wood to protect the bolsters. Open the blade and close the vise on the pivot end. Snug it down and give it a little extra squeeze. Take the knife out and check. It's better to go slow and make a few attempts, because you can easily overdo it. I also don't go past the pivot when putting the knife between the jaws. I like to squeeze only the part from the pivot to the blade end. When you're done, you will probably be able to feel the edge of the pivot on one side. Polish it down if it bothers you. Some folks might peen the end of the pivot pin at this point to keep them from separating again. I've never done that, so I can't help you there.
)