Hi there, Mayra3.
Glad to have you here as a member in the QuickBooks Community. As @JamesDuanT said, the Undo option is only available to QuickBooks Online Accountant users. If you happen to be using the Accountant version and are not able to see that Undo button, you may need to clear the cache and cookies of your browser. The link below will lead you an article that goes in depth on how clear the cache and cookies for QuickBooks Online. I'm here as well to assist with any questions you may have. Simply reply below at any time to contact me.