Not sure what radio you have but should just have to push CLOCK button and then the display will flash the HOURS digit and will say ADJ HOURS. You rotate the DISP knob clockwise to increment and counterclockwise to decrement. When you finish then push the CLOCK button again to adjust Minutes in a similar manner. After that is done you can either push CLOCK one more time to Exit the clock set mode or let it time out.
I thought it is one of the easiest clocks to manually set time on since you have a knob to rotate and can travel in either direction so you don't have to worry about overshooting and having to go all the way around again.