Use a screwdriver to remove dried paint or mildew. Spray the inside of the frame with a mixture of 2 parts water and 1 part bleach. Allow the bleach mixture to sit on the frame for two to three minutes. Wipe the inside of the frame with the cloth to remove any mildew. Rinse the frame well.
Dry the frame with a towel.
Hold the caulk container at a 45-degree angle, and apply it into the groove in the frame. Apply the caulk in a straight line into the groove.
Press the shower door seal into the groove in the frame, and then press it in place. Allow the caulk to dry for five to six hours.