If you have previously exported your emails, calendar, tasks etc from a version of Outlook to a PST backup file, you can use the instructions below to import this information back into Outlook using Microsoft's comprehensive instructions are per below:
https://support.office.com/en-us/article/import-email-contacts-and-calendar-from-an-outlook-pst-file-431a8e9a-f99f-4d5f-ae48-ded54b3440ac