There is rust on the body, suddenly it became a hole around 5MM width.
Do anyone know how to fix the hole?

And advice would be very appreciated.

 

can you add a picture to your post

depends where the rust is


would a 5 mm plastic fastener , rubber bung or grommet fill the hole

get the rusty area to cleanest metal possible and and body filler (bondo /fiberglass )

or weld it up or add new metal