Both Tea Tree oil and Witch Hazel when applied to the fever blister or cold sore can help get rid of the cold sore within a day or so.
The cold sore should start going away overnight though if you apply the Tea Tree oil or Witch Hazel to the cold sore before going to bed and 2 to 3 times per day during the day.
Lemon Balm and even some ice can help get rid of the cold sore.