To refer to a friend,
- Click on the 3 lines at the top left corner to open up a left menu.
- Click "Refer A Friend".
- Enter the details of your friend.
- Click "Invite Friend".
In DUMO, you can also get rewarded for referring your friends! Learn how to get rewarded here: https://dumohelp.zendesk.com/hc/en-us/articles/900006399143-Getting-Rewards-from-Referring-a-Friend