Most filters have a threaded retaining ring. It might be slotted. If you decide to try to tighten it by the slots, use something soft like a toothpick. Otherwise you will certainly scratch it (not serious but unsightly). You might even be able to tighten the whole works by finger. Just grab the filter between thumb and forefinger (with a napkin or something to keep oil off the glass) and twist as if you are tightening a screw. The retaining ring might follow by friction and tighten up as you go.