Salut Vit !
French vowel sounds can be quite tough to master for English speakers, but with perseverance, you will get there!
Normally, the letter combination eu in French has a sound that is closer to "uh" (think of the words eux, feu, jeu, etc.
In the past participle of avoir, however, it sounds instead like the usual French u. For example:
So it's just that exact same sound that you've been working to master! There isn't anything extra or more complicated than the usual "lip-pouting" French u. :)
I hope that this answer has been helpful. Let me know if you'd like more clarification! And if you're really struggling with this pronunciation, I'd say don't let get yourself stuck on it - mastery of the vowel sounds will come with time as you become more fluent and as you listen to more French. Watching more French movies as you've been doing, or listening to French radio stations or podcasts, should help this sound seep into your head over time.
Jusqu'à la prochaine,