Unknown Apple ID in my iPhone

Hello ~ It sounds as if your device is still associated with another Apple ID. If you cannot contact the previous owner ….you will not be able to use the iPhone.Where did you purchase it? Take a look here:

Activation Lock for iPhone, iPad, and iPod touch - Apple Support

Also:

The All Too Common SAD Reality of Buying a Used iPad/iPhone

~Katana-San~

Your phone is not new.

It’s activation locked to a prior owner and will not work again until lunlocked.

See: How to remove Activation Lock - Apple Support