https://plarium.com/forum/en/throne-kingdom-at-war/600_technical-support/39292_syncing-game-accounts-2/ 

Apparently it depends upon where you're coming from, and where you're going to.

Likely @Roger will answer soon enough to help you get where you're trying to go.

If the mean time, you may wish to start a support ticket at http://support-portal.plarium.com/ticketcreator/throne/en?devicelocale=en&spGame=throne-web  - from all accounts, what you are trying to do is certainly possible. They'll be able to help you through it. Seems that between Facebook, Google, and plarium.com , things get a little ... convoluted.

Hello aadesh!

To restore the existing account, make sure it was linked to one of the synchronization services in the Menu > Account. If the aforementioned account was not linked to the synchronization services, and you lost access to the previous device — please contact our Support Team regarding your issue (Menu > Ask a question). They will surely help you🙏

You can find the detailed information about account synchronization by the following link: http://support-portal.plarium.com/en/throne-web/faq/linking-and-restoring-your-account/description 

Have a great day!