Click your unique installation link, and authorize using your Microsoft credentials. Note: this must be done by the account administrator.
2. Add
Add the Retruster ribbon button. In the O365 Administrator dashboard (admin.microsoft.com), click:
Settings > Integrated Apps > Get Apps > Search “Retruster” > Add for all users
3. Enjoy
That's it! Retruster labels will work immediately, and the ribbon button can take up to 24 hours to reflect for all users.