Presoak the garment in cold water for 2 hours. The blood dissolves easily in cold water.
Wash the garment in a cold wash cycle with mild detergent. Do not dry. Heat of any sort can cause the blood stain to cook and possibly make it irremovable.
Check to see if the stain came out. If it did not, then create a paste to remove the stain.
Mix 1 tbsp of meat tenderizer and 2 tsp of cold water. Mix them until a paste is formed.
Spread the paste onto the garment with your fingers. Let the paste sit for 1 hour.
Launder the garment in cold water. If the stain is not fully removed, then repeat the process.