I had a similar thing with my CAAD8. Popped into the West End branch of Evans and they put a new rivet in - 2 minute job. Aluminium frame though, not sure if this would work for carbon. Hope it helps and good luck!
Yeah not sure i'd want to trust evans with sorting this as i think it needs to be bonded to the carbon, tbh i might just try it myself with locktight as suggested above but it might leave it looking a bit DIY.
I had a similar thing with my CAAD8. Popped into the West End branch of Evans and they put a new rivet in - 2 minute job. Aluminium frame though, not sure if this would work for carbon. Hope it helps and good luck!