Edit a line in a file depending on user’s input | Python

I’m working on a contact book application to improve my python skill, so far I’ve created functions to add new contact, view existing contact, but I’m stuck on a function to edit them, I don’t know how to tackle this task (note that editing and adding information is based on user input), currently the only information this application is recording are name, phone number and/or email (if user entered an email).