try installing or loading the package that contains the "undo" function

As an AI language model, I don't have access to your specific programming environment or package manager. However, in general, the "undo" function is not a standard function in most programming languages. It is usually specific to the code editor or IDE you are using.

If you are using an IDE or code editor, you should check if it has an undo function built-in. You can usually find this under the Edit menu.

If you want to implement an undo function in your code, you will need to write the code yourself or use a third-party package that provides this functionality. You can search for packages that provide undo functionality in your programming language's package manager or online repositories.