sorry i do not know of a boat repair place that tightens the rivets
but i have found several videos on youtube that shows how to do it
yourself that might be of help to you. you might check a few out
if you don't find a repair place . https://www.youtube.com/watch?v=NPfPryTRcY4
Here is some other information i saw if you can't tighten them on you own.
fill the inside of boat with some water to mark leaking rivets . and make sure
no seams are cracked. if you can not tighten the rivets drill them out use the
next size larger. Grainger sells "sealed pop-rivets" they are completely sealed and will not leak once installed. I have repaired several aluminum boats with these, I use a small dab of non-hardening caulk on the hole before I install the rivet and then after expanding the rivet with the appropriate tool (Harbor Freight sells the large rivet gun for the bigger rivets) it seals up like a dream and as of yet I haven't had any leak and some of them are going on several years old now.