Refer to article to How to add/edit/delete Test Suite?

1. While in the Create Execution Configuration page, click on Click here to select Test suites.

2. We will be taken to Group List page and select the checkbox for the Test Suites which we need to add to the Execution Configuration.

Note: You can add multiple Test Suites to an Execution Configuration.

3. Click on the Upload button to save the Test Suites selection along with Execution Configuration details.

4. If you want to change Test Suites, go to Edit Execution Configuration page and click on click here to select test suites.