This can be done temporarily by setting another administrator to the same level as an absent administrator .
Details
*Requires operation by the administrator of all rights.
1. Settings > Administrator > Request Approval Flow Settings > Click the row of the department for which you want to perform proxy approval > [Edit]
Click Add Administrator to Same Level next to the administrator's name.
2. In the setting field displayed at the bottom, select the proxy approver name.
3. Click the "Register" button.
Unapproved applications can be approved by the added proxy approver. If you want to remove the delegation, you can remove it from the approval flow by clicking Delete next to the administrator's name .