The wait for Tribunal dates can be a long wait indeed, sometimes holidays are booked.
If the holidays were booked before the tribunal date it is possible to as for a postponement. If this is denied in the first instance, the letter will be in front of the Tribunal Judge to consider again. If this is again denied (and you requested a oral hearing) you can request a set-aside of the decision on not being present (set aside example).
However for reference we include a postponement request template. However keep our disclaimer in mind.