How do I modify curves using plot points?

For this tutorial, we consider that you have created a curve using the 'spline' sketch function.

Now, choose any spline point you want to tweak using 'Select' and then click on 'Move'.

On the left-hand 'move options' window, click on the icon (highlighted below) and this will bring up the XYZ coordinates for the point to be modified. Enter a new set of coordinates to relocate the spline point and the curve to pass through the exact location.

You would need to do these separately for each spline point.

But if you only want to make a rough change, feel free to drag the move handle arrows to modify the curve at each spline point.