Nice Jacket But...

Thin solution of bleach or a cleaner contains bleach. Only way I have ever found of killing the spores so it doesn't just return.

Look out for damp mould spray cleaner, used for house's. I've used that in the past and saved items.

 

As Mr O says you need to kill the source ! You need to kill the mould spore's or the mold will just return ! Only two ways to kill mold ! One will destroy the leather and hence the jacket ! Extreme heat (,burning naked flame) the other is bleach or acids which eat the spore's outer layer(it's skin) and then it dies and won't return. So you need to work out what will do the least damage to the leather and have sufficient strength and effect to kill the mold spore's, it maybe something that will need to be repeatedly done over time !

 

Yep use a bleach solution let it dry out at room temperature then freeze it for a couple of days.

Then apply saddle soap