My dad was using both simcards, now am using both. How can I change the details on the card

Hi Abdulfattah, MTN always assume that the person that registered a line is the owner of the line, you will need the consent of your dad to register the SIM in your name.
You can visit any MTN shop with your dad to re-register the line. You need to come along with your NIN

You can dial *123*7*1# to get information on the location of any of their shop closer to you.
When you dial the code, you will be required to enter your State, then your Local Government Area, you will receive SMS on the nearest MTN office address in your location, or you can use this link: https://www.mtnonline.com/personal/find-a-store/