Here is a background script for restarting a workflow. You can also consider creating a UI action.
var ritm = new GlideRecord('sc_req_item');
ritm.get('sys_id_of_ritm_here');
new Workflow().restartWorkflow(ritm, true);
ritm.setForceUpdate(true);
ritm.update();
mySNstuff.com 
Leave a comment