Can I undo a change someone else made?

Yes. Open the record, go to the History tab, and restore any earlier version - including a version somebody else saved. The only requirement is that you are allowed to edit that record. There is no rule about who made the change.

If several records were changed, you restore them one at a time. There is no way to undo everything one person did today, and no whole-app rollback. Each record is put back from its own History tab.

Restoring does not erase anything. It saves a new version on top, so the version you restored from is still there and the undo can itself be undone. You can preview an earlier version against the current one before you restore it.

History covers the most recent 100 versions of a record. Past that, the screen says earlier changes are not recorded.

A record that was deleted comes back a different way: restore it from the Trash screen.