How to change the status of a trip to open when it is rejected

Hi,

I have a requirement in travel management where when manager rejects a trip or if there is no response from manager , then the status of trip will be changed to " not modifiable". I want to change the status to open .

Any body could help me . I tried with BAPI_TRIP_CHANGE_STATUS , but it is not working .

Thanks and Regards

ravi