Campagnolo chainring bolt stuck to crank
I would underscore taking it to a trusted local shop to remove the bunged screw.

But I would also suggest that if you've tightened the other four that your creak is NOT coming from the chain rings but probably from either your pedal, your cleat or your shoe. Also if you haven't lubed the chain for awhile you can try that as well. 

A creak from the chainrings will almost always be heard when pedaling on both sides. This will also be the case with the crank bolt as well if it isn't properly torqued. 

In one case it was the right LEVER that wasn't tight enough. In another the front derailleur. But shoes and cleats are the most common.