For windows add-in users, follow the steps below:
Close Outlook
Navigate to C:\Users%username%\AppData\Local\assembly
Delete the folder OutlookToJira
Restart Outlook
Login to OTJ Jira for Outlook
Close Outlook
Navigate to C:\Users%username%\AppData\Local\assembly
Delete the folder OutlookToJira
Restart Outlook
Login to OTJ Jira for Outlook