Microsan by prochem..
Put it down, let it dwell, cold water extract ( if you use hot, you will denature the enzymes and then it stains).
The iron might need spotting with rust remover after, and for better results dry it with an air dryer, that way anything that's deep down or in the fibres won't wick back.
Pre-warn the customer that it might not all come out.
Oh and if there is a lot, don't touch it.. leave it to an expert in that field.. Bloods nasty stuff.. telling a customer you can't do it might make you feel awful, they might kick off and it might feel unprofessional BUT it isn't worth the risk.