Rotate a 3D object in OpenGL ES

I have a 3D object rendered in OpenGL ES in iPhone.

When I touch the screen at some point say x-angle from the center. The object should be rotated proportional to the touch and slowly back to the original position.

Can anyone kindly suggest how to do it?

FYI: This is a desktop OpenGL forum, not an OpenGL ES forum. That’s over here, though it’s not exactly the most frequented place on the internet.