Let's say that ALL of the EO churches woke up tomorrow and wanted full communion with the Roman See and denounce their heresies including Papal Supremacy. To whom should they seek out to accomplish this?
"Papal Supremacy"? What's that?
Assuming that they would really wake up, they would accept all Catholic teaching, and realize that the seat of Rome is occupied by an impostor. Like St. Robert Bellarmine said: The Holy Fathers taught unanimously that heretics are neither Catholic nor do they hold any office, and that's by divine law.
They would also realize, that all other seats occupied by the new religion of the new pentecost are ooccupied by impostors.
They might conclude that the time of the consummation of the world has come. Whether they do or don't, they could publicly pray to Our Lord to declare their return, and hope for mercy, like Catholics do.