Identify the damaged area
Remove loose or crumbling wallboard
Cut out damaged sections cleanly
Check for moisture or leaks and fix them
Dry the area completely
Replace damaged insulation if needed
Cut a new wallboard patch to fit
Secure the patch to studs or backing
Tape the seams
Apply joint compound in thin layers
Let each coat dry fully
Sand the repaired area smooth
Prime the repair
Paint to match the wall
Inspect for cracks or uneven spots
Reapply compound or sand again if needed