If a meeting request is declined, the meeting is not saved to your calendar and the meeting request message is moved to the Deleted Items folder.
To subsequently see the meeting on your calendar, do one of the following:
Open the meeting request from the Deleted Items folder, and then click Accept or Tentative. If the Deleted Items folder has been emptied, this option is not available.
Request that the meeting organizer send you a new meeting request. When you receive the new meeting request, click Accept or Decline.