I'd either use springtails or just remove the bark and put it mouldy side up on a sunny windowsill, the heat and light will kill the mould real quick. Or just make some more ventilation holes.
Look around. Under pots, bags, doormats... There are probably several species of introduced or native springtails that will work. I found a dozen in a potted plant and trapped them; now I have a culture of several thousand Folsomia candida that I use in every 'pede enclosure.
Well you'd think that an animal that hides under fallen and potentially rotting logs in the wild would encounter mould a fair bit. If you notice just a few white specks don't worry, if it starts growing fuzzy blue or black mould just change the hide. Or just swap to a hide that won't grow mould like half a terracotta pot
Rocks are usually a bad idea. While centipedes are supple creatures that can be squeezed to near bursting, a heavy stone trapping one underneath it, or even worse, that happening during a molt, would be very destructive. Stick with the bark. The mold will die off soon.
Is it the stuff that clings to substrate and all comes out in one big sheet when you pull away at it with tweezers? That stuff is easy enough to remove. If not I'd suggest lowering humidity for a bit