How do I use my subjects reconquest cb?

I've looked around but can't find an answer.

Ex. I'm playing Austria and have a PU on England, I wanna use their 'reconquest' cb on France, but it doesn't show up as an option.

When I fight France with a conquest cb and try to return cores to England it gives even more AE than if I just take the lands for myself in conquest.

Does it require me to get another damnned dlc or what?