Tomato plant stems are quite resilient and can often heal themselves if left alone. In most cases trying to fix it only does more damage. Since this one is already showing signs of developing adventitious roots above the break it is clearly getting enough circulation past the break and I'd leave it alone. It will likely form a big scab at the injury and keep in growing.

If the top above the break begins to wilt and leaves begin to shrivel then all you can do is cut it off the plant, root the cutting, and let the rest of the plant develop new branches.

Dave

Tomato-broken-stem discussions