Not sure which processor you are targeting (HC08, HC12, ...)?
Anyway after you have created a project using the wizard, the IDE will generate a template for the project.The file main.asm is just a frame for an assembly source file you would eventually add to your project.
In a standard development process I would use main.c (and function main) as starting point for the application and either replace main.asm content with my own code or simply remove the file from the project and add my own assembly source file.
It mainly depends how you want to work.
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