iPhone 12 Pro trade in

Hello! I have recently been gifted an iPhone 12 Pro and would honestly rather have the regular 12! I unfortunately already unboxed it and have used it so it’s technically not brand new, but it’s free from absolutely any blemishes. If I were to trade in this brand new iPhone, how much money/store credit would I get back? Also, do I need a gift receipt or any phone info of any kind to simply trade in the phone? I don’t think I have any of that.