Zoom to Work Area

Grab slider, drag until it fits....  Yeah, I don’t think there is a zoom to fit (unless in keyboard shortcuts!)

Character Animator keyboard shortcuts has all the keyboard shortcuts.

If you mean the timeline panel, there is a zoom control in the bottom right corner (has little picture of small and large mountains on the two ends of the slider). If scene panel, there is a drop down list of different sizes (plus “fit”).