How to remove the Tubi app?

Highlight the icon on your Home Screen, press * on your remote, and choose "Remove app".  If it comes back, it's because someone is adding it to another Roku device that's linked to your Roku account (apps added/removed from one device will be added/removed to/from all devices linked to the same account).  You can see what devices are linked to your Roku account by logging into your Roku account at https://my.roku.com using the email address that's displayed on your Roku device under Settings->System->About.  While you're checking your Roku account online, you may want to add a PIN so that apps can't be added without entering it.