Perhaps Naruto could use his sage mode to sense Anakin's inner turmoil. In sage mode, Naruto has enhanced perception. He could detect the conflict within Anakin and use that knowledge to approach him in a way that would be most effective. He might be able to show Anakin that there is still good in him and that he doesn't have to be consumed by the dark side.
Naruto could save Anakin with his shadow clones. He could send a bunch of clones to distract Anakin's enemies or to create diversions while he tries to get through to Anakin. This would give him the time and space to have a heart - to - heart conversation with Anakin and try to sway him from the dark side.