Accept service name from user during installation

Question

I have created an installer to install windows service. The installer should ask the user to name the service. Hence, I have created a custom UI in the installer with textbox. When user runs the setup.exe file, installation starts and the custom UI shows up. User adds the name of the windows service but how shall i take the servicename as user input during installation and set default service name into service name provided by the user during installation in that custom UI.