If a Clan Leader remains inactive for more than 30 days, the game automatically transfers leadership to the most active Senior Officer in the Clan.
This system is designed to ensure that Clans can continue to operate even when their current Leader is no longer active.

Please note that our Support team cannot manually reassign Clan leadership or reverse an automatic leadership transfer.
If you are back in the game and you no longer own the Clan, try contacting the player who has taken over and asking them to transfer leadership back to you.

You can find more information about the Clan management system in our official article:
https://warrobots.com/en/posts/380