Please help rescue my jam!

Morning,

last night i made blackberry jam, i was woried that it wouldn't set so used jam making sugar and then also grated an apple into it.  The jam has set - too hard!!  is there anyhing i can do to rescue it?  its only a small batch so its not vital.
Also if a jam doesn't set enough, can i reboil it and jar it up again?

Thanks for you help

Thankyou,

will give it a go!

I made strawberry jam and somehow ended up with hard strawberries in light set jam, so to use it up I blitzed it with a blender put it back in jar in the fridge and am using it as topping for natural yoghurt, sort of strawberry sludge