How to make ROI selection automatic

I have a 3d point cloud body with some holes. I would like to use the fitcylinder function in the holes, but to do this i need to select a ROI around the circular shape.

Up to now I manually select the ROI, and it actually work, but I would like to make this selection automatic.

I post the picture of the body i am starting with, but it's geometry could change. It could have a circular shape or irregularity perimeter.

Any idea about how to move on?

roi1 = [0.62,0.67;-0.09,0.11;0.12,0.13];
sampleIndices1 = findPointsInROI(remainPtCloud,roi1);
[ciliner,inlierIndices,outlierIndices,meanError] = pcfitcylinder...
      (remainPtCloud,cyltopointMaxDist,'SampleIndices',sampleIndices1)