How can I unlock my phone from a carrier?

How to unlock your iPhone for use with a different carrier - Apple Support

activation lock is not the same thing as carrier lock.. but you mentioned it, so here is another support article

How to remove Activation Lock - Apple Support

You enter the Apple ID and password used to set it up. If this is a second hand phone, you need to contact them for help with this. If you don’t know the information or can’t get it, you will never be able to use this phone.