I'm stuck - a couple of questions

Rhino Rhino for Windows
1

circular plane

I have this circular plane that has been translated and rotated (see link)
How can I:

  1. move the gimball back to the center.
  2. select a point on the edge where a knot intersects the edge
  3. cut its edge horizontally at half.
  4. extract the edge from the plane
    Without moving the plane, as it is part of a scene.

???

2
  1. Click on the white circle on the gumball & select ‘relocate’
  2. Turn on ‘Knot’ in the osnaps
  3. Turn on ‘cen’ in osnaps to find the center and draw a line. After that, cutting is done with trim or split.
  4. DupBorder
3

@peter harris
After I struggled a little, I finally managed to cut the curve using “cutting plane” icon and split, thanks!