Fresh urine. Best while it's still warm.

How many remedies have you tried so far?

Well, I guess you got it out by now. Next time try egg on it. Let it soak for an hour or whatever. Egg is good for hair and scalp, so won't damage your hair, yet it will likely get the blood soft again so you can then wash it out in the shower.
Or any hair mask you got or can make yourself. Some use honey in combination with something else to make their own hair mask.
So in any case, something you can leave on your hair to soak, that doesn't drip too much (hair mask) and will get the blood soft again.

Using cold water to remove blood will help prevent the proteins in it from staining,
whether it is hair, clothing, curtains, carpet, walls, ceiling, vehicle upholstery, or carpet in trunk
of said vehicle.