How do I fix battery degraded

It appears the battery in your phone was replaced with a battery which is not authentic. This is what happens when non-original parts are installed by 3rd party iFixit type places. If this is your reality, there is nothing you can do. Apple will NOT touch a phone which has been tampered with.

The phone will likely work. You'll just never know the Battery Health on the phone and if you ever have an issue with the phone, you can't take it to Apple for service.