How do I resolve the issue of the compiler not recognising external header files when running project code in NS3.41?

Question

When running project code in NS 3.41, Iam getting an error "no such file or directory"; for include statements of header files that are in the project folder. The header files that are in the LoRaWAN module in the SRC folder of NS 3.41 are not giving this error, it seems the compiler can see these. How can i make the compiler see the header files in the project folder?

I tried inserting the header files with the associated .cc code in the src folder but i continued getting the same error.