Change the ApprovalLink

Change the ApprovalLink

Hi we want to change the approval link from ip to host name ! where we can do this change ? 
the approvallink is now somethink like this   http://78.105.45.26:8080/approval/<some text > 
and we want  to replace the ip to a host name like this http://helpdesk.company.com:8080/approval/<some text >