Use a funnel to fill an 8-ounce spray bottle with vinegar.
Secure the lid, then lightly mist the affected area and wipe clean to remove any surface mold.
Now, spray the affected area again, but let it sit for an hour before wiping it clean with a damp cloth.
Recheck the area and respray if needed.
Notes
Vinegar is extremely effective at killing mold. You will need to be patient and leave it to sit for an hour so it can kill the mold entirely.Always test a small area first before spraying the entire window sill.