Is there any way to seal the one that is. Within a couple of meters I have another step box. With some lid, silicone etc. Let's say the cables pass through there, but cover it outside. Thank you
Remove the part of the box that is rotten and cover with a properly protected 12 x 12 sheet (with anti-rust or hot paint), you can use a lid of the Genrod type boxes that have the treatment described. And seal on the top and side as the friend MJGTSAS says, then paint if you want.