Hi Imanol,
when you have generated two components (first from images and second from scans) then use control points there. These control points should be placed over a whole component and you have to place it on both components. You will need minimally three points, but more is better. The control points should be placed over minimally three images and also three LSP (this is mostly unreachable, because you need to think about this during data capturing). If you will have placed these points, then just click Align and the components should merge.
About the LSPs, did you cut your laser scan in some registration software? This means, that some parts of laser scan pointcloud were deleted.