Literally, unsubscribe from the current email he's using and resubscribe with the new one.  I can't tell you what the unsubscribe or subcribe addresses are, but he can send a message to the help address at each of those groups, or, more easily, just look at the post address and modify the part ahead of the at sign with +unsubscribe or +subscribe, respectively.
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Brian - Windows 10 Pro, 64-Bit, Version 2004, Build 19041  

The purpose of education is not to validate ignorance but to overcome it.
       ~ Lawrence Krauss