Student or Learner
Because our company has to perform the fire maneuvers between these two days. Therefore, we would like to revise our appointment from 14 to 17 March. Sorry for any inconvenience cause
'because" is a conjunction, starting a dependent clause - you cannot have a dependent clause without a main clause. Also, 'as' is the better conjunction.
We regret that we must reschedule our appointment in March, as our company has to perform (the-omit) fire maneuvers on that day. Therefore, we would like to change the appointment from 14th, to 17th March. We regret any inconvenience this may cause.
This is one possibiity. It can be phrased in other ways, and other posters might like to give you their preferred versions.