Inspect the crack to determine its length, depth, and cause
Remove the door if it blocks access to the damaged area
Clean out loose paint, splinters, and debris from the crack
Apply wood glue into small cracks and clamp the frame until dry
Fill larger cracks with wood filler or epoxy putty
Reinforce the damaged area with a wood splint or metal plate if needed
Sand the repaired area smooth after it cures
Prime and paint the repaired section to match the frame
Replace severely damaged sections of the frame if repair is not strong enough
Rehang the door and check that it opens and closes properly