IAR does not recognize tm4c123 library

I'm afraid I am not familiar with IAR so will give general guidance.

You need to make the .h file available to your project.

With IDEs I have used, there were two main ways of doing this:

1. Add the file in the project (or workspace) but it may mean creating a new file copy (so future changes to the header file wouldn't be applied to your project)
2. Add the folder of the header files in the IDE path, so it knows where to search for it. That's the best method, but you need to understand how it works.

I'm afraid I am not familiar with IAR so will give general guidance.

You need to make the .h file available to your project.

With IDEs I have used, there were two main ways of doing this:

1. Add the file in the project (or workspace) but it may mean creating a new file copy (so future changes to the header file wouldn't be applied to your project)
2. Add the folder of the header files in the IDE path, so it knows where to search for it. That's the best method, but you need to understand how it works.