When traveling abroad, the time zone on your device may change, which can cause the data registered during that time—or even previously registered data—to have incorrect dates.
For iCloud Calendar users
Please go to your device’s settings app and adjust the time zone to the correct one. After restarting the device and waiting a bit, check if the date data has been corrected.
For Google Calendar users
Please review and adjust your Google Calendar account’s time zone settings using the link below:
https://support.google.com/calendar/answer/37064
If the issue still isn’t resolved after the above steps, please note that there is no feature to automatically restore the shifted events. You will need to manually correct or re-register the data.
We apologize for the inconvenience and appreciate your understanding.