How can one atone for the sin of perjury in court that led to the loss of rights for a friend's divorcée, knowing that retracting the testimony could lead to imprisonment on charges of perjury and obstruction of justice?

Bearing false witness is a grave sin and a major transgression, especially if it leads to injustice against others. You must repent for bearing false witness. Since the husband refused to pay his ex-wife her rights because of your testimony, you must restore these rights to her if she is alive, or to her heirs if she has passed away. Ask her forgiveness for the hardship and harm she endured because of you.