How do I remove a second name that was appended to a user ID number?

I'm on a NAS and had been running some YAMLs. I have a user ID johnG(1042) G(100) which was used for the YAML. There were some updates along, and I'm not sure how it happened but suddenly it changed to abc(1042) G(100). Now both names exist with the same ID and Group. I did not make the change knowingly and no one else has access to the NAS. Everything seems to be running, but I don't want to wait until there is an issue. How do I get rid of that second name to the same id?