If it just "popped off" then re-insert it into the cone.
Most are just press fit in, that is when you pound on your handle with a mallet, you're pressing it in.
When a chisel sits for a while without being used the wood can dry out with the winter dryness and then then handle may shrink up a little.
This is why it is best to always pick up a chisel by the metal cone, until you're sure the handle is well seated.

If it broke that's another thing.