If you hover over the endpoint of the circle with a move tool, you will be able to find the center point of the circles and do the same for the other part respectively.
In this case I wouldn’t jump to re-doing the model that soon.
Switch the style to ‘X-ray’ and turn on ‘Hidden Lines’ to see all the hidden lines of both objects. Now try moving one object (grabbing by an endpoint) to the target (matching endpoint on second object).
It’s a good exersice.