Remove the overflow cover. Make sure the old gasket either falls away or you can pull it out through the hole. Taking it out is prefered. Put both screws back in the holes then place the new gasket over them and push it into position. Remove one screw and put it back in through the overflow cover making sure it catches the gasket. then do the same with the other screw. Leave the screws loose enough to manuver the gasket into place with one or two fingers. You can hold the gasket in place by pulling on one screw and tightening the other. Once one screw is tight enough to hold the gasket in place tighten the other. Snug them up firmly once you have them both run up. Then don't fill the tub so full.