Link every report to the bug
Attach each ticket to the bug it describes, so that when the bug is fixed you know exactly who to tell.
Wait until the fix is live
Do not message when the fix is merged. Message when customers can see it working.
Write a short, specific message
Say what was wrong, that it is fixed and what to do if they still see it. Skip the technical detail unless they asked.
Ask them to check
A line asking the customer to confirm catches fixes that did not cover their case.
Handle the ones who left
If the customer already cancelled, a brief note can bring some back. Send it once and do not push.
Count what you closed
Track how many reports ended in a message. It shows the team that bug fixes reach real people.