Using a sanding disc or wire attachment in the chuck of an electric drill, remove all traces of paint from the damaged area and an area about 3 cm wide around it. In the absence of the possibility of using an electric drill, the work can be done no less efficiently by hand with sandpaper.
After removing the paint, you can assess the degree of damage to the metal by corrosion and determine whether it makes sense to proceed with the repair or it would be more reasonable to replace the entire panel (if it is possible in principle). New panels can be purchased not as expensive as many motorists believe. It is often much faster and even more economical to install a new panel than to repair extensive damage to the body.
Remove all body trim from the damaged panel, with the exception of those that can serve as a guide to recreate the original shape of the deformed areas (such as headlamp trim, etc.). Using metal shears or a hacksaw blade, remove all loose, loose, and hopelessly corroded metal sections. Then bend the edges of the hole inward with a hammer to form a recess that will be filled with putty.
Use a wire brush to remove powdered rust from damaged metal. If there is access to the reverse side of the damaged area, treat it with a corrosion inhibitor.
Before starting puttying, the hole must be plugged. This can be done by riveting or screwing a piece of tin to the damaged area on its reverse side or by blocking the hole with a wire mesh.
After the hole is closed, the damaged area can be puttied and painted.