These are the steps to activate Tubi on Roku. instructables.com

1.Click the Add Channel button in your Roku's channel shop to add Tubi TV.
2. Open the Tubi app, and sign in.
3.Click the link account t option.
4. Your activation code is displayed on the screen.
5. Go to tubitv.com/activate
6.Log in to your account
7.Enter activation code.
Click on Link Device