The best way to defrost jelly is to remove it from the freezer the night before you plan to use it and place it in the fridge. This will give it sufficient time to thaw while preserving its desired texture.
If you’re in a rush, it’s possible to put your container in the sink and thaw it with warm water. However, this can risk the appearance and setting of your jelly, so it’s best to go for the fridge option, particularly if you have enough time.