Apple TV 4K Rapid flashing white light

That means it's in recovery mode and needs to be restored, since the 4K model doesn't have a USB port you would need to take it to Apple so they can do it. Returns for Apple and most authorized retailers are 15 days, some may offer 30 days. If something was deemed as faulty then the warranty would cover a replacement.

Unplug it for about a minute then plug it back in again. You can also hold down the Home and Menu buttons on your remote. If it still won't come on please take it to your local Apple Store or AASP.

As mentioned there is nothing wrong with it, it just needs to be reset and an Apple Store or Apple Authorized Service Provider can do this for you.