They would start at the bottom again, so it was up to them to climb up just as they had done with the previous ranking they were promoted from.
If they did nothing and relied on past achievements, then it would be quite difficult for them to maintain their position for long.
If they were slow to make achievements for themselves, thinking their previous achievements could be of great help to them, then they would be wrong about that, and they would not make much progress toward rising any higher.
It was usually those who hit the ground running once they were promoted that were able to quickly break past the early stages of their new ranking and to settle in or get closer to the stage when another promotion would become possible.
While there were several different factors involved with the rankings that could let some get ahead of others in the same position, most others started out the same.