External IT Knowledge - Import Content into Outlook on Windows

Select File at the top of your Outlook ribbon.
Select Open & Export > Import/Export
Select Import from another program or file, and then click Next.
Select Outlook Data File (.pst) and click Next
Browse to the .pst file you want to import. Under Options, choose how you want to deal with emails and contacts, then choose Next.
If a password was assigned to the Outlook Data File (.pst), enter the password, and then click OK.
If you want to import the contents of your .pst file into your Microsoft 365 mailbox, choose that mailbox here.
If you don’t want to import into your Microsoft 365 mailbox, choose Import items into the current folder. This imports the data into the folder currently selected.
Choose Finish. Outlook starts importing the contents of your .pst file immediately. When the progress box disappears, the import is finished.
Finally, sync your data to ensure all messages are synced to your new account. Go to the Send/Recieve tab and click on Send Receive All Folders.