No Defrost. Freezer is not defrosting. How can you test the timer or heater to determine the

Question

Freezer is not defrosting. How can you test the timer or heater to determine the cause?HAVE MODEL LG LFC25760SW SER. 605KRBY00485- HEAVY FROST HAS NOW ACCUMULATED IN FREEZER DRAWER. MACHINE ABOUT 1 YR OLD. NO REPAIRS STEPS TAKEN AT THIS TIME.