Start removing broken panels individually next take out damaged panels.
How to fix broken door panel.
To fix your door particularly the garage door be sure to slide each of the broken panel out of the doorframe one by one.
Dribble wood glue into the crack and set a clamp against the blocks to pull the crack closed.
The wooden door panels will develop cracks with the span of time which is more often if the panel is not free to expand and contract.
Insert the spline and clamp the door until the glue hardens.
Clean up any excess glue before it dries but leave the clamp in place for 24 hours.
Depending on the location and extent of wood damage you may or may not have to disassemble the door to carry out a repair i may replace an entire component such as a rail or stile or splice in a new section of a component using a strong splice joint such as a scarf or half lap which also can be doweled if desired.