It's easy enough to trigger Call of Duty Black Ops: Cold War's good ending. During the interrogation sequences with Adler, you just need to tell the truth and reveal that Persues is at the Solovetsky Monastery. From there, you and your team will assault the Monastery in pursuit of Perseus.

For the Good Ending, you will want to tell Adler the truth. You will then be taken to a new mission  The Final Countdown  after which you will be shown the Good Ending. Though whether an ending that sees the main character of a game executed in cold blood really is 'Good' we'll leave to your discretion.