Go to :-
Operating system drive / Usually "C" Drive, "OS C" or "Local Disk C" / etc.
Open "Users"
Open the current User
Open "AppData" "Note you may need to change view options to see hidden files !"
Open "Local"
Open "Microsoft"
Open "Outlook"
DELETE both the *.nst and *.ost files
Open Outlook, these files will be recreated, Outlook wil inform you that it is preparing for first use and you can then manage "Addins", "Plugins" etc