There are two options to undo changes in the same session. A session starts when the editor is opened and it ends when the editor is closed.
Undo changes to layout and content block settings
This option allows you to undo all drag and drop changes (add, move, delete) and changes to content blocks, including modifying of styles, content, formatting and dynamic content.
There is a limit of 25-50 steps that can be undone, depending on the size of your message. (longer messages have fewer undo steps)
Undo changes within a content block
This option allows you to undo granular content and formatting changes within each content block.
Tip: You can also use keyboard shortcuts to undo and redo changes:
Cmd+Z and Cmd+Shift+Z on a Mac
Ctrl+Z and Ctrl+Shift+Z on Windows
Use the version history to undo changes across multiple sessions.