Sterilizing a closet before drying harvest.

There currently isn't any mold but i want to kill any existing spores, or a majority of them. Should i put the 3% hydrogen peroxide solution in a bottle and mix it with water or just put it in the spray bottle by itself?

and if i should mix it with water what should the ratio of water to the 3%HP solution be?

I clean all my rooms, supplies, tubs, pots, materials etc with bleach/water. Let it air out and resume.

Has anybody tried using one of those drapery steamers with AN H2o2 solution in it?