First you need to make sure that there are no valid images on the tape that you want.
NetBackup\bin\admincmd\bpimmedia -mediaid -L

If there are no images that you need, expire the tape:
NetBackup\bin\admincmd\bpexpdate -m -d 0 -host -force
This expires the images in the media database which resides specifically on the media server.

Verify that the images have been expired by re-running:
NetBackup\bin\admincmd\bpimmedia -mediaid -L

Now make sure that the tape is deleted from the volume manager on the master server. This step is automatically run by Veritas twice a day, and if you have used bpexpdate the tape will be removed but you can force it to take effect immediately:
volmgr\bin\vmquery -m
This gets some information on the tape such as its assigned date, pool number and status. If the status is anything other that 0x0, that issue needs to be resolved first – The most likely issue is a Frozen tape – IT must be unfrozen before you deassign it.

To unfreeze a tape:
NetBackup\bin\admincmd\bpmedia -unfreeze -m -h
If the tape was suspended you can replace -unfreeze with -unsuspend

If you are unsure which media server the tape belongs to:
NetBackup\bin\admincmd\bpimmedia -L -mediaid

This step will deassign and remove the volume images.
Volmgr\bin\vmquery -deassignbyid

Finally delete the tape:
volmgr/bin/vmdelete -m

Thats all!!