The nappy should be folded back exposing the cord until falls off. This allows it to air and dry out. You may get the baby grow a bit mucky by doing this but poo explosions mean a risk of contamination of the cord.
Only use cotton wool and warm water to clean the area it if is dirty, otherwise leave it alone.
Avoid using antiseptics unless it has been advised to you by a paediatrician.
Avoid bathing your baby until the separation of the umbilical cord is complete so you don’t disrupt the flora at the base of the cord.