First you type
to list the users logged in. Observe the column "TTY". Remember the values printed there for each instance you want to log out. Next, execute
This also has a column "TTY". Find the process ids (columnt "PID") of the instances you want to kill. Next, you can kill them by typing
where 123 is an example process id, which should be replaced with the correct ones.
Note that the missing session is harmless and will eventually (after one minute or so) go away by itself, so the above exercise is pretty much useless.