Oh My Goodness! I personally would just use a mixture of cold water (NEVER HOT because it could set the stain) and some Dawn dish soap along with a dry rag and a damp rag to blot up to liquid from the couch until the spot is gone. I thought I would look up online what some other ways might be. Here are the links I found. Good Luck with this challenge!
and I found this advice also when I typed in you question verbatim: "...Blood stains are particularly difficult to get off leather objects. A dried in, blood stain may actually require professional care and even then, may not get completely removed. Catch a blood stain early before it seeps into leather and blot as much away as possible with paper towels. Then prepare a soapy solution with detergent and water and pour on the stain. Let it act on the stain for five to ten minutes and then rub away vigorously drying up the leather. Repeat to get better results. Modern detergents contain enzymes which help break away the blood stain. However too much water is bad for leather so you need to dry it completely after the process is completed. If the stain still does not go away completely, try to hide it underneath some polish."
Depending on the color of the leather, hydrogen peroxide watered down with cold water could work. I would try any option on an area of the couch that isn't seem so that you can see what getting the couch wet will do to the leather. Make a "test spot"
Oh My Goodness! I personally would just use a mixture of cold water (NEVER HOT because it could set the stain) and some Dawn dish soap along with a dry rag and a damp rag to blot up to liquid from the couch until the spot is gone. I thought I would look up online what some other ways might be. Here are the links I found. Good Luck with this challenge!
http://www.removeallstains.com/2014/11/how-to-remove-blood-stains-from-leather.html#.WUWWVevyvIV ......
and I found this advice also when I typed in you question verbatim: "...Blood stains are particularly difficult to get off leather objects. A dried in, blood stain may actually require professional care and even then, may not get completely removed. Catch a blood stain early before it seeps into leather and blot as much away as possible with paper towels. Then prepare a soapy solution with detergent and water and pour on the stain. Let it act on the stain for five to ten minutes and then rub away vigorously drying up the leather. Repeat to get better results. Modern detergents contain enzymes which help break away the blood stain. However too much water is bad for leather so you need to dry it completely after the process is completed. If the stain still does not go away completely, try to hide it underneath some polish."
found at website http://www.experienceproject.com/question-answer/How-Do-I-Clean-Dried-Blood-Off-Of-Leather/50723
Depending on the color of the leather, hydrogen peroxide watered down with cold water could work. I would try any option on an area of the couch that isn't seem so that you can see what getting the couch wet will do to the leather. Make a "test spot"