You could try putting something (piece of fleece, toy etc) with the dog’scent on it into your bun’s cage -much like how you do pre-bonding between rabbits. Your puppy is so young now he will be able to accept the rabbit as a family member -but only if the rabbit doesn’t do anything to hurt or scare him. If his experience teaches him rabbits are horrible, that impression might stick. (That’s not necessarily super bad though, it can be good if a dog learns to avoid the house bunny). Anyway, in your case, I think the bun needs to be taught to accept the dog. The reaction from your rabbit is most likely sprung from fear -aggression very often comes from fear (fight or flight-response).
It is true as the others have said, that a dog has a strong instinct to pursue a moving target. I recently learned that the instinct to pursue and the instinct to kill are not located in the same areas of the brain, so pursuit doesn’t necessarily mean an intention to kill. But the stress of being chased can, as Wick points out, cause the rabbit to die of fright. A puppy dog doesn’t have a lot of impulse control, because its brain isn’t fully developed yet.
I have a dog and a rabbit, so it’s not an impossible combination. I did introductions slowly when I got my first rabbit, my dog were 3 years at that time so she wasn’t a puppy. Right now I’m in the midst of introducing a new rabbit in my home, an adult bun that’s not at all used to dogs.