Straightening
Smooth out small dents with a straightening hammer. In this case, you need to put a fairly massive support on the other side. Do not hit the hammer too hard, otherwise the metal may stretch too much and it will not be possible to achieve a smooth surface. When straightening, you need to move evenly from the edges to the middle.
The surface being straightened should be checked periodically by hand until the desired shape is achieved. Small irregularities can then be eliminated with putty.
Rusty spots and old paint residues after straightening must be carefully removed from the repair site. Use coarse sandpaper wound on a suitable block or a grinding machine. Cover adjacent painted areas or plastic parts with adhesive tape so as not to damage them during cleaning.