Back passenger side only floor is soak and wet ..water squirting through matt wh on 1997 BMW 528i

Water squirting through matt whole also

Asked by for the 1997 BMW 528i
You just need to seal it? Use undercarriage coat on the locations underneath and a waterproof marine style sealer inside vehicle like "Goop".
WHERE and WHAT EXACTLY do I suppose to seal..Thanks for the first response
Have to pull up carpet and find where the water is splashing through. Should be a visible hole or rust to follow. Then seal top at this spot and underneath.
I'll try asap....thanks