You want to recharge it. What I've done with a 50 year old soap I have (no scent but the tallow base makes it as good as any soap) is rinse it, use a scritchy brush and do a few laps like you're going to lather, but you're not. After you've done that, quickly rinse the soap and clean out the brush. This cleans the old film that's been exposed for a long time and gets the soap charged to be used once again. You may not have the scent anymore but it should work. Go for it!
I use the wet brush and long loading time technique with old spice soap. It's a great performer, and it leaves the skin feeling nice and moisturized, unlike many soaps.