Follow these steps to manually Export Zimbra to Outlook :-

Steps-1: Open Zimbra desktop on your operating system
Steps-2: Go to the 'Preference' tab from the Menu Bar.
Steps-3: Click on the 'Export or Import' button.
Steps-4: Go to the 'Advanced Settings' tab and select the files that you need to export.
Steps-5: A pop-up window will appear, asking you to save the .tgz file at the desired location. Go to the 'Save File' option.
Steps-6: Click on TGZ file and right-click on the button to extract the files.
Steps-7: After unzipping file successfully, you will get a folder with the same name as shown here: Click on 'OK'.

Hope this helps you out.