Since no one else has responded, this is pretty easy – I take it from your question that you haven’t dealt with rivets much. I think these are held on with plastic rivets. First step is to drill out the old rivets. Use a drill bit the same size as the existing rivet, and try not to expand the hole. Next, get a riveting tool – these are usually < $20. Then go to a good car parts store (NAPA is usually good for this) or a very good hardware store and match them up. The size will be the size of the drill bit that fit the hole, and the depth will be whatever is long enough. It’s usually not a problem to have one too long, but in this case, you might catch things on it.

There’s in general 3 types of material in common use – steel, aluminum and plastic. If it started with plastic, stick with plastic. If it’s metal, I’d go with aluminum – easier to work with. Open up the riveter, and insert the rivet’s nail-like piece into the riveter, stick the rivet in the hole and squeeze. Might have to open it up and squeeze again.

You’ll also sometimes see little washers on one side or the other of a rivet – if it started with these, put them back.

Alternately, if you have a good relationship with a mechanic, give them the $20, and get them to fix it – they’ll have the tools and the rivets laying around.