To begin adjusting individual zones, navigate to the Comfort widget on your dashboard. Once there, look for the 'Advanced Personalization' option at the bottom of the page and select it. Next, scroll down to find 'Custom Contour' and click on it. After that, tap the 'Zone control' tab. Here, you can select each zone individually and utilize the slider to modify the firmness according to your preference.
See the video below to watch this process: