Q: cloud sign in

You have to sign out of iCloud on each device it's signed into and then sign back with the new ID. You may need the old password to do this. (Ideally you should have signed out before changing the ID.)When you sign out your synced data will of course disappear from the device, though not from the server. It will reappear when you sign back in (give it time).

Apple ID email address or password - What to do after you change