From their op-ed in the Washington Post:
Our client’s whistleblower complaint about President Trump’s efforts to solicit interference from Ukraine in the 2020 U.S. election was publicly released a month ago, and since then, speculation about the whistleblower’s identity has only increased.
As each allegation in the complaint is substantiated by new witnesses, the president and his supporters remain fanatically devoted to bringing our client into the spotlight. But the reality is that the identity of the whistleblower is irrelevant.
Much of what has been disclosed since the release of our client’s complaint actually exceeds the whistleblower’s knowledge of what transpired at the time the complaint was submitted. Because our client has no additional information about the president’s call, there is no justification for exposing their identity and all the risks that would follow.