i have experience before.
sad to say, there is nothing u can do, unless its v faint.
cos if its a fairly ingrained already,
if u use whatever formula to scrub away the blue patch, it will always also rub away the base leather color.
so u will either end up w a lighter patch with some blue stains, looks even more unsightly.
i suggest u leave it.
i enquired w leather specialist, say best way is to recolor the whole seat. or wrap again.
that time it was my black leather belt that created a black patch.
this is the negative side to lighter color leathers.
thats why from then on, i always go black leather if possible.