Login to Outlook using Office 365 account. Now, open the folder from where you want to archive emails. Note: You can also perform this action by selecting the specific emails, and then clicking the “Archive” icon on the top pane of the Office 365 account. Select the specific emails and right-click on them. After you turn on archive mailboxes, users can access and store messages in their archive mailboxes by using Microsoft Outlook and Outlook on the web (formerly known as Outlook Web App). The auto-expanding archiving feature in Office 365 provides additional storage in office 365 archive mailboxes.

I hope this information on how do I archive emails in office 365 is helpful. 

Regards,

Lewis