Using a spoon scrape up from outside to inside any lumps.
Multi fold a towel and absorb what you can.
Apply warm water and then absorb what you can, repeat, repeat.
If that works great. if it doesn't and the customer doesn't understand the basics of chemistry (acids, alkalines etc) then leave alone and call someone who knows what they are doing.
If they must use vanish etc then very diluted, then apply water gently rub and absorb, then reapply water until no more foam etc is present.
And that's as far as I ever allow customers to think that they can do it for themselves.
If they do have the common sense to phone me after an accident I will then try and talk them through what can be done with whatever they tell me they have to hand. I once kept a customer applying water via a sprayer for an hour (to emulsion paint) until I got there. Which was the difference between 30 minutes work and possibly hours work if it had set.