Parameterization using environment variables runs a test case automatically multiple times with different input values. The simplest way to make tests more consistent and manageable is to parameterize them, that is, to replace hard-coded input values with parameters. 

Parameterization can be:

• Used to parameterize Test Plan, parameterization using environment variables, Browser, Email Targets, etc.,
• To provide data to build.xml file at run time. 

To add variables to the repository, you can define them in the Secrets tab and use them in the yaml file.  

An example is given below:

steps:
- name: Run build
      Env:
        PLAN_NAME: ${{secrets.TESTPLAN}}

Note: You can access the variable in the build.xml as highlighted below. And, to use your variables as unencrypted, you can directly use them in the yml as highlighted below. For example, PLAN_NAME: Regression.