Hi Rajendra,
Goto Transaction /IWFND/MAINT_SERVICE and click on Add service - Choose the backend system alias - click on Get Services - choose OData service GBAPP_POAPPROVAL and click on it - It will popup asking for whether to store in package assignment or local object. You can choose local object and click on ok. Now the service has been added in your Service catalog list. Assign the system alias and make sure the odata is active and also in SICF.
Hope this helps,
JC