How to quickly soften hard, dried out brown sugar
There are a variety of tips for quickly softening hardened brown sugar here: 10 Ways to Soften Hard Brown Sugar.

The one that worked best for me personally, when I had to do this in a hurry, was to chip off a large chunk of the hardened sugar, put it in a (microwave-safe) Ziploc bag with a damp paper towel, and microwave it for 5-10 seconds at a time until it was soft enough to use.  Don't pierce the bag; the whole point is to allow the steam to re-hydrate the sugar.  But obviously don't leave it in the microwave for too long either, otherwise the bag will either melt from the heat or explode from the steam.  You should also let it cool for a minute or two between zaps; the sugar will continue to absorb moisture as long as the steam can't escape.

I also use the paper towel trick if I need to re-hydrate the sugar the day before.  Place a piece of wax paper on top of the sugar, then a damp paper towel on top, and seal it.  It'll be good as new the next day.  Don't leave the paper towel in there for too long though, otherwise it'll grow mold (doesn't seem like it should, but I personally witnessed it happen).  I like this method because it doesn't require me to waste any apples or bread, if I even have any around.