Change email labels for all contacts' emails to a custom label in one go

I create all contacts in Windows 11 Microsoft 365 and synch them via icloud to my Apple devices.

All email labels in MS 365 are called "Email". The emails get synched to my Apple devices correctly with a label called "email". But on icloud.com, these emails are not displayed in the contacts.

Because of a feature/bug in the icloud app for Windows I am currently forced to work with my calendar entries and contacts in icloud.com.

When I change the email labels on an Apple device from the current "email" to a newly added custom label called "email" (yes, exactly the same word) for a contact, these emails of this particular contact get synched back to icloud.com properly (and Windows 11) and are visible in icloud.com as well.

How can I automate this for all my contacts' emails without having to do it for each my my 900+ contacts?