what information do Danforth and Hathorne reveal to get Proctor to drop the charge that Mary Warren has lied?

They both point out that Heaven is working through the children and the court. They also threaten Proctor with punishment should he not withdraw his petition.

...strike hard upon me that she will dare come here with such a tale. Now, Mr. Proctor, before I decide whether I shall hear you or not, it is my duty to tell you this. We burn a hot fire here; it melts down all concealment.