Set a search range for your algorithm. The search range defines a search area around your selected block. This area will be shown by a red rectangle around the position of the selected block (marked by a red cross). Drag the mouse (movement + left-click) to define an change the search range.
Note:The second image is presented to you now. You define the search range on this image because this is the one where the algorithm will search on.
When finished, click "Next".