R - Commands  
REDO (command)
   Overview   Operations  Commands 

It reverses the effects of previous U command

 Main toolbar: 

 Shortcut menu: If there are not any active commands or selected objects, right-click in the drawing area and choose Redo.

 Command line: REDO

REDO It reverses the effects of a single U command. REDO must immediately follow the Ucommand.