Custom Data by pressing and holding the button

In the documentation I see the following:

Upon pressing the button for more than half a second, you can choose from 4 actions, of which I’m interested in the fourth:

  1. Send custom data to selected ports (up to 32 bytes).

Where in the documentation can I find how to do that?

Go to Device → Settings, select the custom data message mode, enter the data as hex bytes into the input box.