If your Rise of Firstborn account information has already been linked through Facebook, Google Play, and Apple Game Center, you cannot unlink it or change it to a different Rise of Firstborn account.
If you try to link through Google Play / Apple Game Center / Facebook, you will be asked whether you want to import game data linked to the account.
If you want to create a new Rise of Firstborn account, be sure to link it to the Google Play / Apple Game Center / Facebook account that does not have an interlocking record.