Undo function - InDesign

I am not sure if I can post my question here. I got this link from one of the courses for InDesign. I am hoping someone who can answer my question regarding InDesign here. ( The issue I encounters is very elementary.) I can’t find “Undo” function in InDesign! (LOL) I looked at Edit tab, there is no listed function of Undo. I search all tabs, menu. None of them have a Undo. I used the short cut of “Ctrl+Z”. It don’t work, too. I did the Google search. They all said Undo is under the Edit tab. Help! Thank you.