How to "UnAuthorize" a threat I accidentally authorized instead of manually deleting. Yes, I did screw this up.

On Mac Air, OS 10.11.6 - Ran Sophos AntiVirus 9.5.3 - It found threat & showed in Quarantine.  Quarantine said can't Auto remove, need to manually remove.  Went to web sit to see how.  I am not computer literate.  When trying, In Error, I hit the Authorize button for the detected file and threat file disappeared.  My mistake, I thought I was unlocking the file to manually remove.   How do I "Un-authorize the threat" so I can get it back & remove it.  Can this be reversed.  The chat person on Sophos said I should address to you.  Thank you for your help.