You can add Send Anywhere Outlook 365 Add-In from the Office store.
Add Send Anywhere Office 365 Add-In

After you add Send Anywhere, you can use the Send Anywhere Add-In by clicking the Send Anywhere icon at the bottom right of the Outlook 365 Mail Compose window.

If you don’t see the Send Anywhere icon, turn on Send Anywhere in Outlook 365 Mail settings > Manage integrations > My add-ins.