5 years ago my wife and I went to Yemen to work as doctors. Unfortunately, under some pressure from the owner of the medical clinic that we were working in we used to perform (ultra sound examination) for a lot of people. Most of them were unnecessary plus we did not know how to do a correct ultrasound examination. We used to have a share from any ultrasound performed. There is no way to know the people we did the ultrasound for. Please tell us what we should do for God's forgiveness.

Praise be to Allah, the Lord of the World; and blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.
No doubt that your previous practice includes many forbidden acts such as:
1. Demanding patients to undergo an ultra sound examinations without having any necessity for it.
2. Performing the ultra sound without having accurate knowledge.
3. Unjustly eating the money of people.
4. The sin becomes more offensive if the exams you performed caused harm to the patients.
Therefore, it is compulsory for both of you to make sincere repentance for that sin. A condition of making repentance is repaying the rights of people. So, it is possible for you to find those patients through the lists of the clinic if there are any in order to pay them back their money.
If it is impossible to know the patients then you should give that money in charity on behalf of them intending that its reward will be in the account of those people not your account.
Finally, you are obliged to offer sincere advice to the owner of that clinic and inform him that doing so is forbidden. Do ask him to make repentance for his ill practice and to immediately give up cheating patients. If he does not accept your advice then threaten him that you will uncover his treachery and defame his clinic.
Allah knows best.