First create a emailid which is little different from previous ( alter one character, can be changed later )
Go to the backup directory and change the name of the emailid from the backup which needs to be restored ( new mail id which you just craeted )
Now create a file named email.txt and enter a emailid which you just created
Its time to restore a backup now , in order to perform that use the Following command

for i in cat /path/email.txt; do zmmailbox -z -m $i postRestURL "/?fmt=tgz&resolve=skip" /path/zimbra-bkp/$i.tar.gz ; echo "$i -- finished "; done

You are done the email has been restored to newly craeted mail account

Next thing you have to do is rename a Newly created mail account to the previous one.