You will need to use Legacy Outlook in order to use the Import function. Click on the Outlook menu to see if there is a checkmark beside Legacy Outlook. If not, select it. Outlook will relaunch and you will be able to continue.

Outlook for Mac can import data from an older version of Outlook, an OLM file exported from Outlook for Mac, or a PST exported from Outlook for Windows.

1. Click File and choose Import.
2. Select the option for what you would like to import and click Continue.
   
   
   
   
3. Browse to find the file, select it, and click Import. 
   
   
4. Click Finish. You can find the imported data under On My Computer, which you can then move to an existing account on Outlook.