Start removing broken panels individually next take out damaged panels.
How to fix broken door panel.
Dribble wood glue into the crack and set a clamp against the blocks to pull the crack closed.
Mount the new panels finally set up the new panels on your garage door.
Put extra care so that you do not damage more panels.
Insert the spline and clamp the door until the glue hardens.
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.
Clean up any excess glue before it dries but leave the clamp in place for 24 hours.