In the Point Clouds dialog (Drawing > Attach > Point Cloud > Point Clouds dialog launcherView > Home > Primary > Attach Tools), select the point cloud file you want to clip.
Click the Clip Point Cloud tool (Drawing > Attach > Point Cloud).
In the tool settings, click the Slab icon.
Set Mode to Boundary.
Enter a data point to define the start point of the clipping block.
Enter a data point to define the length of the clipping block.
Enter a data point to define the height of the clipping block.
Enter a data point to complete the clipping operation.