I accidentally rejected a request. Can I restore it or return it to another status? 

If a recipient is rejected in error, the recipient can be added back to the request by following the instructions found here: Updating Recipient(s) Post Submission - Approved Request

If a request activity is rejected in error, it cannot be reversed. The submitter must create a new request and resubmit it for approval. 

A request admin can cancel rejected requests by following the instructions found here: Admin Functionality to Cancel Requests