Remove any screws located near the leak, using a screwdriver. Clean away rust with a wire brush and replace the old screws with stainless steel ones. Use a new screw that is larger than the old one so it fills in and seals the hole. Take the old screw to the store with you so you can compare it to the new screws. Old screws can cause leaks as they rust or become corroded. Stainless steel screws will last longer.
Clean the awning surface to remove any dirt or grease with a general cleaner, such as dish soap. Rinse and dry the area carefully with a towel. Apply aluminum sealing tape along the leaking area. This works well in a pinch and the repair can last for months.
Wash the leaking area and after it dries, apply a line of polyether sealant to cracks or gaps in the awning. Use a sealant that is UV resistant, exterior grade and designed for seams and metal. The sealant will fill the crack as it dries and plug the leak.