If you are using Lighthouse Studio, in the CBC exercise dialog, go to the Attributes tab, then click the Prohibitions button. Next select the Advanced Prohibitions tab (which you can read about here: https://www.sawtoothsoftware.com/help/lighthouse-studio/manual/hid_web_advanced_prohibitions.html).
Suppose that you have brands 1-5 and it's brand 1 that you want always to be present. Make sure brand is your first attribute.
Now, in the advanced prohibitions specify that a between-concept prohibition that has 8 columns: attribute 1 level 2, attribute 1 level 3, attribute 1 level 4 and attribute 1 level 5. This tells the software that no choice set can have exactly the combination of brands 2, 3, 4 and 5.
Next, be sure to use the Complete Enumeration design strategy and in the design tab check "additional settings" and finally select the check box for "Show levels of first attribute no more than once per task." Generate your design and check that this works.