After manually defrosting the freezer I installed both a new defrosting element and a new defrosting thermostat. The only difficulty is that the video on your channel did not mention the metal guard that fits over the heating element. The guard fell out when I removed the element and not knowing its purpose or position I installed it under the heating element.
The next day I found on another appliance youtube channel (fix.com) an explanation of where and how to affix the guard if it happens to fall out. So the day after watching that video I reinstalled the heating element with the guard above it.