Use a new tungsten carbide bit in a battery drill to take the heads off the rivets, get new riverts (stainless) from any hardware supply house.
There may be a single phillips screw under the unside trim that anchors obe side, after that its use a piece of wire to saw thru the sealant. Use any decent solvent to remove the remaining sealant but be careful not to soak the area as any remaining solvent will screw up the paint job.

I have had luck freezing or chilling sealant and removing it. Tey using any of the commercial freeze sprays(used to test computer boards) to turn the caulk into frozen licorice and then peel it off.