In a plea you must confess to your crimes and of course your apology and you won't do it it again. For example if I were banned for xray my plea would look something like this:
Example plea: "I was banned on (insert date here) for xraying, I now realize my mistake of doing this and I promise not to ever use xray again, I do understand that if you do decide to unban me that this will be my final chance, if I were to get caught xraying again I understand that I will be permanently banned with no chance of plea."
It must be in your own words and you must be convincing. I wish you the best of luck