Hi there I am Joel and will be helping you with this today,
You need to replace both the temperature sensors in the unit there is one in the freezer and one in the refrigerator replacing both will save you from having problems with one or the other in the future, just buy 2 of these:
Refrigerator Temperature Sensor
Part #: 12002355 - click here
If you only want to replace one then replace the one in the refrigerator section to fix your issue of the refrigerator getting too cold.
here is a video that shows how to replace both of them:
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