How to retrain growing tip of Cornus controversa Wedding Cake Tree
It's a bit difficult to advise without seeing it, but if the original leader is still in good shape, you could prune the dominant shoot back, and nip out some of the buds that appear on it over the next few months. That might well divert the tree's energy into the original leader.
What a lovely tree, by the way. I have often admired it - saw the variegated one at Overbecks National Trust Garden near Salcombe last year (what an amazing garden / house!!), but I can't afford it!! £50 minimum, for a small one.