If it's an accessory belt and it's already squealing, simply tightening it is not the answer. Once belts start slipping the rubber gets "glazed" from the heat build-up. It loses traction and becomes more prone to slipping and the problem gets worse and worse. Honda came out with those "self-tightening" belts... what a joke

If you over-tighten the belt to compensate you can damage the engine.... seriously in some cases. You can wear alternator bearings out prematurely, for example. I recall a case years ago where a PS belt was over-tightened on a 92 Civic and it snapped off the end of the crank after a few months. Matter of fact, Honda went to a wingnut tensioner bolt instead of the hex head so wrenches and air tools could not be used.

Anywho, if you're sure it's a belt, go buy a set of accessory belts and replace them all. Make sure you properly tension them according to the factory service manual for your car and you'll be all set.