Sabb Radio/Clock

Have a friend who has a 95 Sabb 900. It has two clocks. One is the digital in the radio and then to the left of the radio is a digital one. The clock radio is correct but the analog one is incorrect. It is off about 2.5 hours. When you try to adjust one it adjusts both. He has no owners manual. How can he correct one without affecting the other ? Thanks