Using Amadeus flight search API, how does my users search for flight when they don't have location code

I am using amadeus flight search API, built the endpoint with PHP and tested on postman, working perfectly now i am worried about how my users will use the frontend to search for flight, do they have to know the city codes to be able to search for flights? I want a situation whereby they just entered the names of the cities in the form from my frontend and they get to search for flights not entering city codes

Thanks everyone for the contribution, i am really grateful, though i discovered getting list of JSON data of IATA codes, cities, and countries in my frontend application and then using javascript filter to search through responding to the onChange event handler from the user's form will solve the problem, once again i appreciate everyone contributions, i am really grateful