1) Logon your zimbra server and undeploy the zimlet
2) Create a folder called _dev under
then create org_alfresco_zimbra under the _dev folder
and then unzip the zimlet zip file to that org_alfresco_zimbra folder
Once you unzip the files, run following commands
chown zimbra /opt/zimbra/mailboxd/webapps/service/zimlet/_dev/org_alfresco_zimbra
chown zimbra /opt/zimbra/mailboxd/webapps/service/zimlet/_dev/org_alfresco_zimbra/*
The above approach actually deployes the zimlets as dev mode so no restart is needed.