All the possible positions of the value 7 in four different cols are in the same four rows. Because the number of cols matches the number of rows, and because each col must contain the value 7; each row will have a 7 in one of the intersecting cells.
Hence other possible positions of the value 7 that are in the rows but not in one of the cols can be removed.
Therefore we can remove A6-7, C6-7, F7-7.