With a different slug
You can easily login as a different user on a different nation. Simply go to the menu and logout. Now enter your new slug and follow the normal login process.
With the same slug
In order to login with a different user on the same nation, you will need to uninstall the app completely and then reinstall. Now you will be able to login as a different user using the same nation slug.
We're currently considering making it quicker and easier to switch accounts. If this would be helpful for you, please reach out to us and let us know!