Other than in Java a launch configuration for the C code generator must be created.
From the Run menu select Run Configurations
Within the dialog select eTrice C Generator and click the New button to create a new launch configuration.
A new configuration should be created. Name it _gen_HelloWorldC_ and add the model via one of the add buttons.
In the Refresh tab select The entire workspace
In the Common tab select Shared file and add the HelloWorldC project via the Browse button.
Apply your changes. The new configuration should now exist in your workspace.