You are running some risk. There isn't any you can "sterilize" it without killing everything. You could, I suppose, pull everything apart, bake the substrate, and soak the plants in IIRC, potassium permanganate (?? - aquarists use it), and bleach the glass. Then, add new isopods and spring tails.

Easier to just start over anyway.
Or, just accept the risk. Not recommending that, just sayin'.