How to use Allegro on Code Blocks?

I have installed Code::Blocks and found that Allegro 5 is in the games repo.

I got allegro 5 from there, added the repo and did a zypper install but how do I tell code::blocks to use allegro?

If you’re looking to customize the code of an application,
You generally need the application <source>, not an installed application which is usually pre-compiled (unless it’s entirely script-based).

When I’m investigating an app with an intent to modify the application code,
I generally look for the application’s project which today is often hosted on an SVN or git site(There are others like Mercurial and CVS).
If it’s not found immediately with an Internet Search,
I look for the application’s website which often provides a link to source.

If you do install a source package from an openSUSE repo,
You need to determine the location of the files… one way is to query the package for the files, ie

rpm -ql* source_package.rpm *

However you obtained the source and determined its location on your machine, <then> you can point your IDE to those files.
Be sure to read the source documentation which will generally describe how to build, typically describing required dependencies, tools and often a recommended procedure.