Some situations with large volumes of blood may require replacement of the cushion.
If the blood is only in the face yarns, often an alkaline prespray or protein spotter plus lukewarm water (100 to 120 F) will clean it out just fine. Do a little flushing.
The next step up is an enzyme product such as an enzyme prespray or Bio-Modifier. Allow some dwell time. Flush with luke warm water.
A stain remover with hydrogen peroxide such as Urine Stain Remover will get it if the above methods don't. Or you can skip directly to the hydrogen peroxide product.
As Harry Hides offers, sometimes enough iron in the blood to leave a rust stain after other methods have been used.