Have him email the local league coordinator for help. I forget who I had to contact but I went through this process myself when I got into league tennis.
He will have to make a case that he overestimated his ability, back it up with evidence as to why he believes this to be true as well as his overall tennis experience and ask to be rated a 3.5
I was successful and got dropped down, was still a "self rate" though so you are still subject to the 3 strike rule.
Here's an example of how I made my case:
Dear Sir or Madam,
I recently joined USTA to play league tennis and went through your self rate process. Unfortunately I have overestimated my ability as in the matches I have played I have been unable to win as many as 3 games in a single set and most of my sets I lost at 6-0.
I did play tennis in high school, however my school was not strong and we never made it to post season play. Since then I had not played for 8 years.
I honestly do not feel I can be competitive at 4.0 as my record shows. Furthermore I was not even asked to play on my club's 4.0 team as they feel I am not ready for that level.
I ask that you re-self rate me as a 3.5 please.
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