There is usually a drain in the freezer ( necessary because of course the freezer defrosts itself periodically.) That line takes the water to a pan located under the condenser coil/compressor area. The heat from those items evaporates the water. Your line is plugged...a fairly common problem. You need to find the line....starts somewhere on the floor of the freezer...and blow it out. Or it may have an ice clog in it.