How to properly use "User_Select_Setup.h" in my project?

[dbyy]

Hello,
I'm trying to use TFT_eSPi library for some of my projects (ILI9488) and I'm trying to figure out how to properly use the User_Select_Setup.h file.
What I understood so far from reading, using this header file will overwrite the definitions in User_setup.h.
For example: my hardware is a Arduino Nano32 with a ILI9488 TFT.
I figured out that for this configuration the header file "Setup21_ILI9488.h" would be correct configuration file.
But I don't know how exactly to activate this header file in my project.
Do I have to add an include somewhere in my
a) application code or
b) do I have to modify my sketch code
(or is there any approach for that)?

I couldn't find any clear explanation in the whole library folders on Github.
I would appreciate any advise that helps me.
TIA