A: First,
you should ask for Allah's forgiveness because of lying and denying a person's right, turn to Him in sincere repentance, regret what you have done, and be determined not to commit this again; and may Allah accept your repentance.
Second,
you should do your best to find the inheritors of this man and give them his due right. If you are unable to find them, give the money as Sadaqah (voluntary charity) on behalf of the man. If you find the inheritors, give them the choice of either taking their money, and you will be rewarded for this, or accepting your deed of giving the money as Sadaqah and they will be rewarded for this. (Part No. 14; Page No. 151) May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.