Import PST file in Existing Outlook Outlook Data File

Use this option if you want to migrate Outlook messages, contacts, calendar items, tasks, and notes from one machine to another machine. You can create new PST file or import all mailbox items in existing outlook.pst file format.

• First of all click on file tab and choose Open option
• Now click Import or Import/Export.
• In Import and Export Wizard, choose Import from another program of file option and clock Next button

Now Choose Outlook Data File (.pst) and go ahead with Next Button

Now click in Browse button and select desired files to Import

In options, please select Do not import duplicates option unless you want the imported information to replace or duplicate items already in Outlook.

Now click on Next button and check include subfolder option and Finish

Read More Steps of MS Outlook