With the Accessport installed navigate to the "gauges" menu.
If it's the first time you've gone to the gauge menu of the Accessport it will prompt you to ask how many monitors you want to display. The selection can be updated later in the Gauge Setup menu.
From the main gauge display, you can simply hit the center button on the Accessport in order to start logging. If you haven't pre-selected anything there are default parameters that will be logged which are typically the ones COBB Customer Support will ask you for. Note that the Accessport will show "logging" at the top of the screen and at the bottom will let you know the logging rate.
In order to stop logging, you'll need to hit the center button on the Accessport again.