At the bottom of the page in edit mode scroll the toolbar menu to the right until you see the left & right arrow keys [undo/redo].
If you have a bluetooth keyboard
ctrl+z | ctrl+y
If you don’t have a physical keyboard you can use the Hacker’s Keyboard as explained here.
You can also set Hotkeys for undo & redo[in case ctrl+z & ctrl+y aren’t to your liking]
There is no “undo” for file name changes that I know of.