As a new rust user, I may not know every mechanic that Rust Playground offers. But I need to know how to use the undo option in Rust Playground?
Do you mean the usual text operations like undo and redo?
If so, the editor is exposed as a textarea, so the usual text operations of your browser work.
That's usually something like Cmd/Ctrl-Z or available in the Edit menu of your browser.
If the usual undo/redo operations don't work, maybe you configured the playground to use different key bindings. You can change the setting in the top right corner, by clicking the "Config" button to open a drop-down menu with the "Keybinding" option. If the value is set to e.g. vim or emacs, the undo/redo key bindings of those editors will be used, which is different from the usual Ctrl-Z/Ctrl-Y.