Name the impact without exaggerating it
Describe who had to wait, worry, redo work, spend money, or make a choice with incomplete information. For a message about how to reconnect with a former book club, use this factual base: name the group, your earlier role, why you left, and the current point of contact you found.
Make repair practical
Offer the repair you can actually complete, with ownership, timing, and any limit stated honestly. 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.
Let future behavior carry the proof
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. A promise inside a message is weaker than a visible change in what you do after it.