1)
What did Moshe tell the people?
1.
Rashi: He repeated to them what Hashem had said to him - "ha'Yad Hashem Tiktzar"? And it was following the people's negative response 1 that he gathered the seventy elders.
2.
Oznayim la'Torah: He told them to prepare for the next day 2 - when their request would be fufilled.
2)
Why did Moshe change the order - first telling them what Hashem had told him nd then gathering the seventy elders?