By default, once you log into the app you will remain logged in. This is to ensure that the app is quick and easy to use.
However, you can log out of the app if you want to.
First open the menu by selecting the three lines icon at the top of the screen
At the bottom of the menu, select "settings"
Now select the "logout" icon (a door with the arrow exiting)
Then select the "Sign Out" button
When you log back into the app, make sure you use the same method every time... So if you logged in with a "social account (Google, Apple or Facebook) select the same option when you login.
Similarly, if you registered using an email address and password, make sure you log in with the same email address and password.