I've just tried the Toshiba UK support page here:
https://www.toshiba.co.uk/innovation/generic/tv-support/
It's got a REALLY annoying woman talking on it but (by searching 'remove banner at top of screen' in response to her question) she says that you need to reset your TV:
"To reset the TV, please follow the steps below (please not, some TVs have different menu structures, so these steps may vary).
Press the Menu button on the remote
Choose the Install and retune menu and press OK
Choose First Time Installation and press OK.
A box will appear, asking if you are sure. Select Yes and press OK to continue.
Your TV will now reset. When it turns back on, it will give you some quick prompts to get set back up and will then scan for channels."