It looks like the de-frost drain pipe is clogged. The most common reason for the clog is ice itself. So here's the plan. Empty the freezer(I recommend emptying the entire refrigerator) and have a close look at the back. You should notice the freezer wall which has to be removed to be able to see the defrost drain pipe. Take a Mug of water heat it up to medium temperature(Do not use boiling water as it will melt the pipe) and slowly pour it into the pipe. This water will melt any ice that is inside and clear the path for the water to flow down the pipe. Continue this procedure until you see water coming out of the bottom of the pipe and into the tray that collects water from the pipe. If problem persists, let me know.