I need to change the control points size in ROI
Where and How can I control this size
You cannot modify Annotation ROI control point sizes. However, in recent Slicer Preview Releases you can create markups ROIs and use that for cropping volumes. Markups ROIs have adjustable control points size and other advantages (e.g., they can be rotated).
Control point sizes can be modified in ROI markups, which replaced ROI annotations.