up in my attic today... found black mold.

All along one side... growing up inside plywood surface. about 2 feet
up. Unsure if it is down below insulation. Black in color, but not
shiny. If memory serves,"shiny" black is really nasty stuff. I think
this is common stuff/

No other evidence of water damage, did find bathroom fan vented into
attic... lots of people live in house, so lot of humid air has been
pumped up there, Could that have caused it?

New roof about 7 years ago, no evidence of leaks.

No respiratory problems noticed in house.

What is first move after properly venting bathrooms, would like to
mediate it myself if possible. can I toss out old insulation, wash
down with bleach & replace insulation? What else needed?,