where do I find my 4 digit reset code for my iPhone 6 plus 9.0.2

Where do I find my 4 digit reset code for my iPhone 6 plus iOS 9.0.2. I am no longer able to connect my iPhone 6 plus to my macbook pro since I updated to iOS 9.0.2. I love my apple stuff but struggle with some of the software and it's logic!! Help😕