Reinstatement comes into consideration, the application is time-bound.
If the appeal deadline was missed without fault of your own, an application for reinstatement can be filed. The relevant provisions are Section 71 AVG and Section 33 VwGVG. The application must be filed within a certain period from the removal of the obstacle.
Set out the unforeseen or unavoidable event in a comprehensible way and make up the missed appeal at the same time.