What version of SEPM are you running?

Check here:

Using the Risk log to delete quarantined files on your client computers

How to delete Quarantined items from the Symantec Endpoint Protection Manager.

Hi,

please check below link.

http://www.symantec.com/docs/TECH106444 

Please Fallow the below steps for SEPM.

1. Log into the Endpoint Protection Manager.
2. Click on the Monitors tab on the left pane.
3. Click on the Logs tab at the top of the right pane.
4. Click on Risk in the Log type drop-down menu.
5. Select a time range from the Time range drop-down menu. (The default is Past 24 hours.)
6. Click Advanced Settings in the bottom left hand corner.
7. Next to Action Taken: choose Quarantined
8. Click on the View Log button. This gives you a list of the quarantined items.
9. In the Risk Logs window, click on the risk(s) you would like to remove.
10. Click on Delete from Quarantine in the Action drop-down menu.
11. Click on Start.
12. Highlight the item and confirm deletion.

OR...

Delete quarantined files on SEP clients

https://www-secure.symantec.com/connect/forums/delete-quarantined-files-sep-clients

How to Manage Quarantined files.

http://www.symantec.com/business/support/index?page=content&id=TECH106443&profileURL=https%3A%2F%2Fsymaccount-profile.symantec.com%2FSSO%2Findex.jsp%3FssoID%3D1375960534484eKDZpBx182VQ391Rhr66MIX3kOPqzcXJrKM6S