My AppleTv light keeps blinking and there is no display on the connected TV. Not sure how to update the firmware since I have no iTunes account etc

AppleTv light keeps blinking […] Not sure how to update the firmware …

A flashing status light is a sign that the Apple TV box failed to start up properly. First try a cold restart (disconnect from power for a minute or so). If the issue persists, then the system software may need to be reinstalled. For the Apple TV HD A1625, users can do this themselves, by connecting to a computer through USB. See the detailed procedure here: Restore your Apple TV - Apple Support. Restoring the system software will reinstall the latest version, and also wipe any previous user information on that device. Start over with a clean slate.

• If your computer is a Mac with macOS 10.15 or later, then the connected device would get listed in the sidebar of a Finder window, under Devices, at some point during the procedure (step 6).
• If your computer is a PC with Windows, then get the iTunes application. Then the connected device would get listed inside the iTunes application, for restoring (step 6).
• If your computer is an older mac (macOS 10.14 or earlier), then use the bundled iTunes application. Then the connected device would get listed inside the iTunes application, for restoring (step 6).
• If you can't restore your Apple TV yourself, then take your Apple TV to an Apple Retail Store or Apple Authorized Service Provider for more help.

… I have no iTunes account etc

Every Apple TV box should be registered with the Apple ID account of the (main) user. An “iTunes account” is an Apple ID account that is complete enough that it is ready for iTunes Store/App Store transactions. It seems that you have this device signed in with your account listed on your account. Any Apple ID account would need complete users information as asked, including name, DoB, country (state), a verified email address (respond to test message), and a valid payment method (if you get apps or services that cost something, or may cost something later on (in-app purchases, subscription options).

The iTunes application brings access to the iTunes Store (music for buy or subscribe, movies for buy or rent, TV shows for buy) on PCs and older Macs, and can also collect your other music and videos, and is also very versatile for Apple ID account management. Account management can alternatively be done on the web.