About the calendar
Just log in and use your device with the same Apple ID and it will be synchronized automatically. If the sync doesn't work, go to the Settings app on your iPhone or iPad and select the Apple ID Please turn on the "Calendar" section.
To check your Apple ID, open the Settings app on your iPhone or iPad and click on Apple ID, iCloud, iTunes Store and AppStore at the top of the screen.
If you're using Google Calendar, go to the "Settings" app, "Passwords & Accounts". Add your Google account from and make sure "Calendar" is turned on please.
ToDo, Notes and Diary data sync
There is a fee, but by subscribing to the premium service, you can use iCloud backup Data synchronization is enabled by Create an iCloud backup on a device with the latest data, overwrite it, and then select the device you want to receive the data on Now, if you restore your iCloud backup data, it will reflect the latest data.