Hi Emma,
Thanks for providing me with that information
If you “Update Timezone Data”, it will most likely not automatically change the time of all of your events, however it will enable you to have additional timezone options.
Once enabled, you can opt to set the timezone per site or per event, which may be helpful for you.
In addition, you will want to set the WordPress timezone under Settings < General to the correct timezone as well.
Here is more information on working with timezones:
https://theeventscalendar.com/knowledgebase/time-zones/
Let me know if you have any other questions on this topic!
Thanks,
Jaime