modifying contacts in c phonebook program

i am writing a code to create a phonebook using c language. This project has: display, save, load, modify, delete, add , search, exit functions . I stuck with the modify one and this is the required Modify function will prompt the user for last name and then you should list all matching contacts and let the user choose one of them to be modified. Can you tell me how to do it?

i am working on the code to get the last and first name and reenter the contact after modification but i am not sure at all about if it satisfies the required or not