A clogged defrost drain tube is not necessarily the cause for water collecting in the bottom right corner of the freezer. You did not mention any other problems with the refrigerator or the freezer. I recommend that you have a service technician diagnose and repair this problem in your refrigerator.
Accessing the evaporator in this type of refrigerator is not easy. If you still want to access evaporator and the drain area underneath it, you would need to
unplug the refrigerator
, remove the ice maker, the freezer drawer, the rails and then remove the back grill as shown in the image below.
If you do not feel confident repairing this problem yourself, then you can have it repaired at your home by a Sears technician. Here is a link for the website:
Sears Home Services