Mould/ damp caused by shower leak

[ILOVEALLCAKES]

We had a loft conversion with en-suite completed 2 years ago. Over the last few weeks have noticed a very small area of water post shower.
DH went into 2nd loft (tenement loft) and can see the chipboard flooring is black with mould suggesting this has been an issue for a while.

Builder came today, chopped off a section of skirting board. Photo shows the back of the skirting. He also lifted the Karndean floor tile. Has re-sealed the shower, including the upright frame which has never had sealant and said this will all be fine once it dries out. DH concerned as internet search suggests removing everything covered in mould.
WWYD in this situation?

if the leak has genuinely been fixed, expose all the wet material (remove floor coverings, and floorboards if possible) and it will be dry in a few days.

If you have a desk or room fan (not a fan heater) perhaps you can position it to blow cold air into the damp cavity. This will cause it to dry faster by evaporation.

if you are anxious about mould spores, you can scrub them with bleach in water, with a little detergent. Do it again once they are fully dry. Dead, dry mildew is easier to clean off than living. After scrubbing you can sponge it off. Wear rubber gloves.

You can spray a mould killer onto surfaces that you can't reach if you want, but it will die when dry.

There always mould spores on the air and on surfaces, everywhere, throughout the world.