Controlling the Regional Ruler
The Valyr Lordess and her subordinates would have died without Michael. He achieved the 'impossible' by killing the 106 Lords and clearing the Savannah Region. That was something nobody managed to do in the last few decades. It was a fantastic achievement and the reason Michael could make ridiculous demands of the Valyr Lordess.
First, he told the Valyr they had to eliminate the remaining soldiers and Awakened, who continued roaming the Savannah Region. Their corpses had to be brought back to Michael.
Since every Lord had an average of 100,000 Soldiers and they killed less than four million over the last few days and weeks, there were still millions left to kill.