My phone battery is dead so I installed a new battery. How do I install and know that the battery is genuine?

• If you bought a battery to install yourself, it is NOT authentic
• Apple does NOT sell parts to anyone
• Opening your phone to do a DIY battery replacement will prevent you from EVER getting any support for your phone from Apple. We can't help you either
• It is a BAD idea to self service iPhone
• You are on your own here

How can replacement new battery

Apple will not help you because you tampered with the device.