The HIP system process for requesting pre-approved OT is 2-step (1. employee submits OT pre-approval request and 2. supervisor approves/denies).  Many departments have different processes for getting budgetary approvals for OT that involve special workflows, forms, memos, etc.  Your department should continue all of those processes as required outside of HIP.  Once budgetary approval is set, the employee should login to HIP to request their specific number of OT hours for the days they intended to work.
Click here to learn more about how employees submit OT pre-approval requests.