If your Alliance's Leader has been inactive for more than 1 month, then a designated Officer can be voted in to this position by fellow Alliance members.
While viewing the member roster, an Officer can initiate a voting period by tapping on the "Replace" button next to the group's inactive Leader. Note that this button will only appear for Officers.
If an Officer receives more than 50% of the approving votes from fellow Alliance members, then that Officer will become the new Alliance Leader.
Please be aware that Customer Support is unable to mediate or make changes to Alliance leadership. If you believe your Alliance leader and/or Officer(s) will not be returning to the game, then you may wish to get together with the current members and reform your Alliance.