Make room for the other version
Ask what the other person understood before assuming that you are arguing about the same facts. For a message about how to reconnect with an alumni association, use this factual base: name the group, your earlier role, why you left, and the current point of contact you found.
Correct the record precisely
Correct only what you can support, acknowledge any real impact, and propose a practical way to prevent repetition. Ask whether rejoining or visiting is appropriate and follow the group's present process. Make the immediate next step clear enough that the recipient can answer without reconstructing the entire history.
Agree on a testable next step
Do not claim an old role, skip current rules, or pressure a volunteer to resolve historic conflict privately. Use safeguarding and formal leadership channels for discrimination, abuse, threats, or vulnerable members. Do not recruit an audience, publish private evidence, or turn a misunderstanding into a campaign about character.