HI
The only thing you can do is rip it out and replace.
Even a steam cleaner at 115C will only get some out.
It gets ingrained and becomes part of the silicon.
Please don't waste your time trying to clean it!
I would charge about £55 to do this job, chances are it will come out in one piece, scrape any residue off, clean area, wait to dry, renew, tell them not to use for 12-24 hours.
Regards
Martin
