Right! First time with a new technology is always unnerving. So, get a small drill bit and drill out the little dot in the middle of the rivet...
Usually the rivet will just fall off but if it does not, some gentle prying with the blade of a flat-head screwdriver or the edge of a pocket knife will lift the rivet out.
When it is time to put it back in, you will want to go to Lowes or Home Depot or Harbor Freight etc. and get one of these...
I have this exact same model. Got it at Lowes. It works great. You will also need some rivets. Since your mast is aluminum, I'd recommend getting aluminum rivets and not stainless or brass.
You stick the skinny end of the rivet in the tip of the rivet gun where I have the red arrow... the fat end goes in the hole in your mast where you removed the old rivet. Now just squeeze the handle a few times until the stem you stuck into the gun breaks off. The gun pulls on that stem and as the stem pulls upwards, the part that is inserted into the mast expands and creates a "dam" behind the aluminum wall of the mast. That holds the rivet in place. Sometimes the rivet activates but the stem does not break off. If that happens you can just bend it back and forth until it breaks off. If you are still unsure, find a youtube video and watch one being done. Once you see it, you won't be worried about using a riveter. They are really nice to have and you find all sorts of things to fix with them once you have one in your took kit.