- Turn off the TV and unplug it from the power.
- Push and keep pushing the OK (the central round key) and the BACK (⇽) button.
- Without releasing the remote keys, plug the TV to the power and wait for the Recovery Screen to appear. Do not release the keys until the Recovery Screen appears (if you're unable to enter recovery mode this way, read the alternative method below).
ALTERNATIVE METHOD TO ENTER RECOVERY MODE
If the previously described method to enter recovery mode doesn't work for you, there is another way to do it using a Windows PC connected to the same LAN/Wi-Fi. Go here ->
https://xdaforums.com/t/tool-all-in-one-tool-for-windows-android-tv-tools-v4.4648239/ and download the Android TV Tools V4. Follow the instructions on the site to install it and connect it to the TV. Once installed and connected to the TV, select 7, then X, then 10, then 2. The TV will reboot into Recovery Mode and you can then follow the above instructions to install a new firmware.