Thanks again. Because I've messed with cars/trucks for over fifty years, I've learned to plan ahead. I bought three new plastic rivets when I picked up the mudflap.

Only a $1.24 a piece and I am quite likely to mess up at least one. For sure I would have messed up all three by just trying to pry them out. The mudguard listed for $103.06. I paid $80. Mighty pricey if you ask me, but Toyota parts are still cheaper than the parts for my Harleys but not by much.
I am ready -- I have both a 10 mm. socket wrench and phillips head screwdriver.
Tom
Update : I broke all three rivets. Suggest if you have to replace a mudflap, buy the rivets.