Does the engine run? It can not run if the harmonic balancer is spinning on the crankshaft. For that reason, I assume you're turning the entire crankshaft which can easily be done with hand tools. That means just the outer ring has come unglued from the center hub. That will affect only the operation of the serpentine belt, nothing else. There is no fix for that. The balancer must be replaced. If you try any type of repair attempt, it absolutely will not be successful. When that ring flies off, the crankshaft position sensor will most likely be destroyed along with anything that ring hits. Think of it as potential shrapnel.
You would be smart to replace the belt too. You might get away with reusing the old one but the grooves are much more sensitive to improper wear than on the old V-belts. It is very likely to cause a squeal or chirping sound from the wear.