I first slip a piece of rubber shelf/drawer liner between the vent and the bowl. Hold one side of the vent flat against the bowl with one hand while tapping the opposite side flat with a small ball peen hammer. Keep working around the vent until it flattens out. I've used this method many times and have never chipped any porcelain. Then use a set of long needle nose pliers to bend the tabs back straight. Just make sure you bend at the fold and not bend the entire vent up. Or, bring it by my house next time you come through the area and I'll fix it.