To undo changes in Vim, you can use the u command. This will undo the most recent change you made to the file.
For example, if you delete a line of text by mistake, you can use the u command to undo the delete and restore the line of text.
You can also use the Ctrl-r key combination to redo a change that you have undone.
In addition to the u and Ctrl-r commands, Vim also provides a number of other commands for managing changes to a file. For example, you can use the :undo command to see a list of all the changes that have been made to the file, and the :redo command to redo a specific change from the list.
You can find more information about undoing and redoing changes in Vim in the Vim documentation by typing :help undo within Vim.