Cannot erase iPhone from iCloud
Long ago I used Gmail as my AppleID, let's call it "email 1".
I then changed AppleID into iCloud email, let's call it "email 2".
Today I tried to erase an iPhone by logging in iCloud on a web browser and accessing this URL: https://www.icloud.com/find/. However, when I clicked "Erase iPhone", the browser dialog showed up and asked me for the password which is associated with my "email 1". Of course there is no way I can proceed because there's no longer "email 1" attached to any iCloud account.
Note: The dialog did not allow me to change the "email 1" into "email 2", it simply asked me to enter the password. And my current AppleID's password would not work.
Any suggestion would be really appreciated.
iPhone 7, iOS 13