Hi Ashok ,
This has been discussed before in multiple threads .Closing the manually created reservation is possible through MBVR , I think your aim is to delete the reservation. MBVR is the T code .
http://scn.sap.com/message/7706863#7706863
As far as making the quantity 0 is concerned you will need a LSMW preferably with a BDC recording to update all the components . A recording on IW3K will be easy then IW32 because IW3K will take you directly to component screen .
I am not aware of any mass change option of Components in standard SAP .
Anjan