On iOS, You simply have to select "Log out" option from the Settings section.
On Android, You have to clear the game's cache and data from Your phone's by going to Settings -> Applications -> Landlord GO and selecting specific option there.
After loging out of one game account, You can play the game on other account by loging into different Google Play Games or Game Center account and launching the game.
However, we strongly advise playing on only one account, since using multiple accounts by one player is considered cheating.
IOS: If there is no "Log Out" button, try tapping then tapping and holding game's logo in quick succession.