Open the Sidebar (swipe from the left or tap on the hamburger menu to the top left)
Click on the Settings icon (gear icon to the top right of the sidebar)
Open the connection that you want to delete. Click on the "3 dot menu" in the top left and then select "Delete connection".
You can choose to Keep or Remove transactions previously imported by this connection. Be aware that removing all transactions imported by this connection is irreversible! (You can of course, add a new connection).