The Labels page allows you to add new labels, and rename or remove existing ones.
1. Open the Configuration page by clicking on the three dotted button, located on the upper-right corner.
2. Head to Configuration on the left panel, and click on Labels.
3. Input the Description, then click on Add button.
3. Optional: Delete your custom Label. If your custom Label is being used, you will need to set a new label for the affected Test Cases.
4. Optional: Delete unused labels.