thanks for reaching out! In short, there are some shortcuts:
"r": Reset the view to the original view point before being adjusted to the current geometry
"a": Reset the view to fit all objects (default view)
"u": Changes to an upright view of the current scene
Additionally "w", "f" and "l" trigger different navigation modes which are sometimes nice to play around but not very helpful when you work with the viewer e.g. select / hide entities etc. We might disable them in the future. You can get back to the default mode by hitting "e".
I added an issue to put this information to the documentation as well. I will update the issue when this is available with the corresponding link.