Is expiation obligatory for one who changes his testimony in court after having taken an oath, and what is the expiation for this sin?

He who witnesses the Fajr prayer in congregation should not distort the truth and deceive himself by combining false testimony with a perjurious oath, for Allah has linked them with polytheism and idol worship. The worst in rank among people in the sight of Allah on the Day of Judgment is a servant who lost his Hereafter for the worldly gain of another.

Therefore, one must hasten to sincere repentance to Allah, increase in His remembrance, and draw closer to Him through righteous deeds. Sincere repentance erases what came before it, and he who repents from a sin is like him who has no sin.

Part of perfect sincere repentance is expiation for the perjurious oath (the false oath), as a precaution and to avoid disagreement. If retracting the testimony results in the loss of a right, then it is legally binding to restore it to its owner, because the false witness must compensate for what was lost due to his testimony.