Add-in Deployment Instructions - O365 Administrators
Go to office.com and Sign in to the admin account, and then click Admin:
Next, click to expand Show all:
Then, click to expand Settings:
Now click Add-ins:
Click Deploy Add-in:
Then click Next:
Copy this URL:
and paste it into the manifest file URL field. After pasting, click Upload:
To finish, Assign users and then click Deploy (screen-capture not shown). After deploying, you can close this window.Note: It will probably take about 24 hours before the add-in appears in Outlook.
When the add-in becomes active, users will be prompted from within Outlook to complete their signature profile.