Dear Bala,
1) I assume that you are talking about the MWI (Message Waiting Indicator) light (or message icon) on the end user's phone device. And i believe for some reason this light is continously blinking. If this is the issue, then following is the resolution,
Resolution: Dial the 'MWI OFF' number from the user's phone. Following is the path to locate it,
CUCM --> Feature > Voice Mail > Message Waiting
2) If you are referring to actually deleting the voicemail messages from the user's voicemail box, then there should be a Unity server or Unity Express. You will have to login into this device.
For Unity Server:
UNity Server --> Subscribers --> search by extn
Access the voicemail box --> Empty or Delete the voicemail messages
For Unity Express
Unity Express --> Users --> search by extn
Access the voicemail box --> Empty or Delete the voicemail messages
Hope this helps.
Regards,
achilleus