Hi
You said "I reserved the Work item" .... does this mean that there were multiple recipients, A, B, C and You? And now you want this WI to be available to all again - A, B, C and You?
If yes, just go to SBWP-> Inbox->Workflow->select the WI and press the "Replace" button:
using this, the work item will not be reserved with you anymore.
But if you want to forward it to some other user, who was not the original recipient, then I Would go by Rick's advice to contact the WF Admin
regards,
Modak