Tips for sterilizing soil/substrate

unfortunately some of the substrate I bought was not sterilized and most definitely came directly from a forest. So now there are a bunch of tiny critters and potentially harmful bacteria in the soil. It’s too much to throw it away as it already has been mixed with a base substrat, flake soil and white rot wood.

its very unfortunate for the potential critters in the soil but I don’t want to harm the isopods (I already got a surprise species that got brought along)

does anyone got some tips on sterilizing/disinfecting small batches of soil? Oven is a bit hard as I only have one tub for the substrate and I don’t really want to have another or dirty the oven with substrate when I inevitably spill some