Notice how the second syllable of “eaten” contracts till the vowel disappears completely. To do this, your tongue must stay touching the top of your mouth, behind your teeth, for the /t/ sound, and then for the /n/, without moving between the two sounds. When you make the /n/, you just let the air out of your nose. Practise it a few times.
You might say this after a heavy meal, or a period of too much eating, for example, Christmas.