Some pretty good suggestions here, and I'll toss mine in. Use a lubricant/all around protectant called Ballistol. It's an all natural oil that's been around a hundred years or so. Smells like stinky feet (the smell goes away after a couple of hours), it will kill the mold as well as nourishing the leather without over softening it...and if it's moldy, the leather needs some conditioner. It also adds some water resistance on the way. It's the only thing I've used on my 20 some year old cycle leather from "Back in my earlier Punk Years", and it's still in stellar shape. Actually, it's in better shape then I am.
Oh, here's a link:
www.balistol.com. It's an item every prepper should have, as it's mighty versatile for wood, leather, metal, electrical connections, etc. Don't prep without it!