They do have an interference fit on the crank snout, so you will need a puller to remove it and if the crank was drilled and tapped, then a correct balancer installer could be used to re-install it. With the engine in the vehicle, it will be slow going and tough trying to tap it back on with a hammer(not recommended though).
It will need to be removed ASAP and replaced, it is only a blink away from slinging off the end of the crank if you can move the outer ring by hand. There have been fatalities before from them coming off with the engine running, so don't start it up again!
