Have a lg lfx25960st has frost on back wall of

Older freezers have a mechanical timer that shuts the cooling unit off and activates a heating element to melt the ice that forms on the cooling coils next to the fan. Newer ones control it with a circuit board. It sounds like yours is not defrosting and the ice buildup has stopped the fan. Or the fan could be bad and without the airflow thru the cooling coils they are covered with ice.
You need to remove a cover inside the unit to get to the fan, cooling coils, and defroster heating element. There could also be a thermostat attached to the heating element that will need to be checked.
Unplug the unit, disconnect the heating element and check for continuity ( with an ohms tester ) , it should give some reading on the tester. You will need to talk to a repair shop to get the exact ohms it should read. If you have a friendly repair person, they will tell you how to check everything out.