Tightening the screws on a flute is unlike tightening screws on anything else. There is always a level of variety in the tightness among flute makers and different models. You can’t hope to take a simple screwdriver and tighten the screw as much as you can. Your best bet is to take the instrument to a trained and experienced technician, because they will know how to tighten the screw properly. While you wait for your instrument to be serviced, avoid playing it for a while until the issue is fixed.