how to get in to a iphone 6 without a apple id

IF you mean that you need the Apple ID and password in order to activate the device, there is no way around it. If you bought the phone from someone else, you need them to help you unlock the device.

They need to go through the steps in here.

What to do before selling or giving away your iPhone, iPad, or iPod touch - Apple Support

If you are talking about something else, you need to explain it in detail in very clearly.

If an iPhone is protected by Activation Lock, you will not be able to use it unless and until the previous owner removes that lock.

More information:

Find My iPhone Activation Lock - Apple Support