As somebody that has owned many beagles I'm gonna tell you trying to train a hunting dog to not hunt is not gonna happen. You might curb it while you are around but as soon as your back is turned what it was bred to do is gonna come back out.
You can either get a different dog or make sure the dog can't get to the chickens.
You can either get a different dog or make sure the dog can't get to the chickens.