In order to teleport your Capital to another Kingdom, the clan Leader would need to use the Clan Capital Teleport to another Kingdom item which level coincides with your current Capital level.

Click any tile on another Kingdom’s map you would like to move your Capital to, then click "Teleport":

Purchase the necessary item and click "Use":

Note that the higher the Capital level, the more the teleport item will cost.

Using the teleport item does not teleport your clan Capital directly! Rather, you teleport your city to the chosen tile. Immediately after confirmation, all of your clan members except for the Leader will be kicked out of the clan without triggering the 14-day rejoin cooldown, while the game page will be reloaded:

Immediately after the game reload, you will be able to place all clan buildings to any desired tiles on the map of the selected Kingdom, starting with the Capital:

For placing Forts will be deducted additional building resources from your account. The number of resources depends on how far the Fort is located from the Capital.

Your clan members will not be teleported to the chosen Kingdom.

Note that if your Capital is being upgraded, then you will only be able to buy the Teleport of its current level. Be cautious: in this case, once you finish upgrading the Capital, this item will no longer be available for use since your Capital level would change!