Hello Sky,
Could you please try below steps, it works for others
Close Outlook. Type or paste this into the address bar of File Explorer then press Enter:
%localappdata%\microsoft\outlook
Delete the ost - name format will be emailaddress - you'll see the file extension only if you have the option enabled to show extensions (on View menu in file explorer)
The other way to find it is, with outlook open, right click on the top level of the data file - this is usually your email address - and choose Open file location. This opens file explorer with the data file selected. Close outlook and go back to file explorer and delete or rename the ost file.
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Thanks,
Mohammed S