Surely it has to be lashings of water?
If you don't know what it is, then trying to counteract acid with alkali could backfire badly.
Milk could introduce bacteria, and the old wives tale of butter on a burn has been debunked now so I doubt it would be advised here.
Dilution and washing off must surely be the way.
If no plain water is available then the any water based liquid has got to be better than nothing.



