Very confusing instructions. I am giving you some links below which will help, but I will explain this particular one.
I am not quite sure what you mean by “The function control key label (icon)”, so I am assuming you mean the rectangular label keys at the bottom of the screen. If you want to change the component name, instructions are given in the link below.
To use the procedure on page 24, you have to be in the Learn mode, but you must hold the key down for 2 seconds to enter the label mode BEFORE you have learned anything on that key. The idea here, I guess, is that you can assign the label before you teach anything to the key, and then teach it, if necessary.
If this confuses you, go to the normal labelling process:
Commander off/muting
Press the Set key at the top of the screen
Press the Label key at the bottom of the screen
Press Compo (or System or Timer)
Press the component key
Press the key you want to label
Label and exit when done
These threads will answer your questions, and others which may arise.
RM-AV3000/3100 NEWCOMER’S PACKAGE-WELCOME-CHECK THESE OUT (IF YOU HAVEN’T ALREADY DONE SO) AND SAVE YOURSELF SOME PROBLEMS AVOID SYSTEM CONTROL PROBLEMS HOW TO LABEL, CHANGE OR HIDE BUTTONS CHANGING BATTERIES (May not apply to RM-AV3100-time will tell)
AND IF YOU HAVE A SONY RECEIVER: CHANGING YOUR RECEIVER AND REMOTE TO AV1 (or AV2) COMMAND MODE