Step 1.
Go to the Design tab of your project and click Add warm-up sample button.
You can decide to add a warm-up sample to all the sessions or a specific session.
Based on the options chosen, the warm-up sample will be added to the first position of each set in your design.
In the product properties, you will see an extra product with number 0. Which means that no data will be collected for this product. You can customize the warm-up sample, for example name the product to use in placeholders.