In the Microsoft 365 admin portal navigate to the Integrated Apps section.

Upload a custom App.

Choose Office Add-in at the App Type, and https://app.tonicdm.com/outlook/office365.xml as the link to the manifest file.

Click Validate, then Next.

Choose whether to deploy to the Entire organization or only to Specific users/groups.

After accepting the permissions and confirming the deployment, it usually takes 1-3 days for the add-in to appear in Outlook.