There are several ways to approach this problem. First, is your father in good to excellent health? Or does he see himself as being in "fair" or "poor" health? This is important because studies show that patients who rate their health as "poor" are more likely to die.
Self-assessed health is also a strong predictor of how much function improves after surgery. People who say they are in poor health end up seeing the doctor and using medications more often. The cost of health care goes up quite a bit for these folks.
Are your father's fears based on past experiences? Perhaps he's had previous surgeries that didn't go well. Finding out the root cause for his fears may be the place to start.
A good physical exam by his doctor before the operation is a good idea if it's not already part of the preparation for the surgery.
Encourage him to talk to his doctor about his concerns. Perhaps there is a medical reason behind his fears.