I am relatively flexible in general (ie able to do a backbend), and when I'm doing a split with my right leg in front I can bend backwards and touch my head to my thigh pretty easily. I cannot do the same with a left split.
What are some stretches to target one side of my back?
Sounds like you are already really flexible - which should make this easier! I actually have the same struggle (only that I am less flexible lol) but my right side is definitely way more flexible than my left side.
So I decided to now work on my weak side with help of my favorite stretch - after generally warming up my back, I go for the standing scorpion (or yours might already be more of a needle) just for my weak side. Also you could use a wall placing your bad leg up as in needle pose while your other leg has the knee resting on the wall (foot leaning up the wall) and push your body up with your hands on the floor. You can also practice pigeon pose just with your bad side. Even doing your split on the floor while leaning back - pretty much every one sided back bend exercise will do while you just focus for a while to invest more time and effort on your bad side rather than the good one!
