Can you use Bloodbending to heal a person?

While there is no canon answer to this, there are fan theories that healing and bloodbending are different applications of the same skill within waterbending. This is why Katara was able to pick it up so quickly when we first see bloodbending, and

Bloodbending can be seen as not just controlling the flow of blood through a body, but also controlling the flow of energy or chi. So bloodbending and waterbender healing both work through the same ways as a subset of waterbending skills. Healing is just a gentler, more specific level of control while bloodbending is total domination.