Do you mean it has hardened into a hard big powdered clump? Or do you mean how to soften your laundry with a liquid softener? In case you are talking about a powdered ball that is formed, I would take the hard powder out of the box and into a bin or bucket and try crushing it with a potato masher or hammer to get it back to powder form. You might want to put into a Tupperware container so that moisture doesn't get to it instead of back into the box that it came in.. If you are talking about a liquid softener to soften fabric, I like the snuggle and downy brands.
Put a slice of fresh bread in the hard detergent. Put lid on and leave it overnight. Same way with hardened brown sugar!
Yep, bread will work for hardened powder detergent, the same way that it softens rock hard brown sugar.