If those are solid rivets, you can just use a hammer to mash them, which expands the shank into the hole as well as mushroom the head. Be sure you have something solid to back up the other side. You could even use a center punch right in the middle to expand them, but that's not really necessary. Think of a rubber eraser that expands sideways of the direction that you compress it.
If they were semi-tubular rivets you can get rivet setting tools designed for them to roll over the rivet end against the material.
Rivet setting tools You can also get them on Amazon that are made for use in an air hammer.
