#include "SDL.h", as shown in SDL Image, is the way you should include SDL headers, so the answer to your question is to adjust your include paths till that works.
If you had previous code that worked by doing #include <SDL2/SDL.h> or similar, that is not the recommended way AFAIK and you should change that to also be #include "SDL.h". Unfortunately there are many tutorials out there that recommend the wrong way.
For more info see this previous answer: #include "SDL/SDL.h" Vs. #include "SDL.h" - #5 by Vittorio_Giovara
Or this blog post: SDL2 common mistakes and how to avoid them