1997 Isuzu Rodeo center cap on wheels

I had some new wheels put on my 1997 Isuzu Rodeo today, now 3 out of 4 of my center caps are loose and noisy when driving. I noticed one was loose when I picked up my truck (didn't notice the others until driving) and asked the installer if they could tighten it up somehow, the man said he didn't know what to do and suggested I remove them or replace the lug nuts. How do I get the center caps to fit securely to the wheel. I am planning on taking my truck back to the installer, but I would like to know how to install them in they can't or won't fix the problem. Any help will be appreciated. Thanks.