How do I bypass someone else's Apple Account and use a new one on my iPhone XR?

In most cases the proof of ownership is going to be the original purchase receipt from Apple or Authorized Apple seller. The receipt will have to show the Serial number or IMEI number on it. Providing Apple that information yourself will not do any good.

You cannot remove an Apple Account from a device without the password. That prevents others from taking your account off of your device and resetting to the phone to make it theirs. That is why you are now in the position of providing the documentation to prove you purchased the device. Since Apple does not get involved in any third party sales, a receipt from another source will likely do no good as anyone can create a receipt and it would not prove they own the device.

You can't bypass it, it’s doing what the security feature is designed to do. You can submit proof of ownership to Apple following https://al-support.apple.com/#/additional-support