Question

How do I run codes on other than the default 'main' tab?

Answer 1

Other tabs present in same IDE specifies the multi file project.
Such as in C, you can create custom header file and can include in main or other file.
Here is brief example
https://www.onlinegdb.com/blog/introducing-multifile-project/

Answer 2

Create another .c file and use that. Make sure nothing is in main.c file, especially header files or it won't compile.

Or

create your own header files by creating a file with .h file extension and in main.c call the .h file by #include "name.h"

Your own .h file can store functions and data etc