How to restore (put back) a Calendar event from Trash in Outlook

For example, if you deleted a meeting from your Calendar, you cannot simply Undo this action. To restore the removed event, do the following:

   1.   Find the deleted meeting (or deleted appointment) in the Trash folder, for example:

   2.   Do one of the following:

• Open this deleted event and in the Meeting (Appointment) dialog box, on the Meeting (Appointment) tab, in the Actions group, click the Copy to My Calendar button:
  

  In the Outlook message dialog box, click OK:

  

  Notes:

  1. Do not select the Copy the meeting option as you will not be able to see your replies and updates for this meeting.
  2. This approach will send your confirmation to participate to the organizer again.
• Open this deleted meeting and in the Meeting dialog box, on the Meeting tab, in the Respond group, and then:
  
  • If you already accepted this meeting, select the Accept drop-down list and click Do not Send a Response:
    
  • If you already replied using the Tentative option, select the Tentative drop-down list and click Do not Send a Response:
    
  • If you do not answer for this meeting yet, answer as you want.
• Right-click on this event and select Move -> Calendar in the popup menu:
  
• Right-click on this event and choose Move -> Other Folder... and then in the Move Items dialog box, select Calendar:
  

See also this tip in French: Comment restaurer (retourner) un événement de calendrier à partir de la corbeille dans Outlook.