Find out whether the organizer means this Thursday or every Thursday
Read the wording of the change. “Thursday this week because the hall is closed” gives you an exception. “From September, lessons will run on Thursdays” gives you a new pattern with a start date. If the message says only “see you Thursday,” ask which dates are affected. Do that before editing several months of entries or telling the person who usually collects that their recurring duty has changed.
Inspect the dates on both sides of the change
Suppose a coach changes practice for the holiday week. Move that practice, then check that the following week still shows the usual day. If a new permanent series starts next month, give the old one an end date. This prevents two practices appearing every week after the switch.
Check reminders and journeys attached to the old series
The lesson can be correct while the old pickup still repeats on Wednesdays. Look at the first changed week as the driver or collector would see it. Move the travel reminder and any genuinely linked duty, then check that unaffected weeks kept their normal arrangement. If the calendar invitation belongs to the organizer, use their revised invitation as the source rather than generating a second invitation for the whole household.