I have had good luck with Arm and Hammer baking soda disks in combo with dryer sheets. I usually place the disk inside the bag and the dryer sheets outside the bag. Then I put it in a dust bag for at least 1 month. Patience is a virtue. I have had even the smoky smells come out that way. I have a lot of very old clutch bags (even from the 1960's) that I collect. I have also sprayed Febreze on the lining as well (always a test a small area 1st).
It's easy. It's a smell that doesn't come off when you wash the bag. I know that people tell not to wash bags and I agree because not every bag is the same, several bags have leather parts which can be ruined by water, and you have to be extremely careful!
Usually, if a bag has, let's say, the smell of perfume or sweat or any other thing... it can be washed away.
With mold, you can wash it 10 times and it's still the same smell.
Perseverance is the key. It's not going away in 1 or 2 days, but if you keep using baking soda, coffee beans, even sunlight and wind (even though sunlight can damage the bag) for sure the smell will GRADUALLY but eventually go away.