Is there any tool or script that can select hard edges? I want to select my hard edges and make them soft. Does anyone have any ideas?

Do you mean edges marked "hard" by the user , or edges that are shaded "hard" automatically?
___

for marked edges, there's the "crease edge" filter, for the automatic edges, use rctools

I meant the first one and thanks, I didn't know there is a crease edge filter, that's great to know.

On the right where you see the arrow icon, object, point etc buttons. There is a tiny button below with a triangle in it. Click it and select your filter.

Thanks, I found it