You can soak it in a bucket of water for a few hours or longer until it is soft and pliable and then dry it off with a towel, put crumpled up newspapers underneath it to help absorb water and to shape it and then wrap packing tape around the sadlle to hold it in the final shape you want it. Let it dry out at room temperature for a few days and then remove the tape and paper and apply either proofhide or other leather dressing as you would on a new saddle.
I have a great wife and she gave me a new Brooks for Christmas. Now from everything I understand about it, it should not get very wet. I know the old saddle is very dry, but soak it in water? Won't that make it curl like a dog chew when it dries?
TJ