You cannot edit the End of the Previous-Segment :
The motion-law of the Previous Segment is a Dwell or a Constant-Velocity.
You want the Position and Velocity of the Selected-Segment to flow from the END of the Previous-Segment.
Because, the Position of the Dwell motion-laws is specified at the START of the Segment and not the END.
The Position and Velocity of the Constant-Velocity motion-law are specified at the START of the Segment and not the END.
Thus, you must:
1.Click the Previous-Segment (that is the segment that is the Dwell or Constant-Velocity motion-law).
The Previous-Segment instantly becomes the Selected-Segment.
2.Edit at the Start of the Segment, the Position if a Dwell motion-Law, and also Velocity if a Constant-Velocity motion-law.
When the segment is a Dwell motion-law, the Position at the Start of the Segment is also the Position at the End of the Segment.
When the segment is a Constant-Velocity motion-law, the Position AND Velocity at the Start of the Segment are also the Position and Velocity at the End of the Previous Segment.
These motion-values flow to the Next-Segment when Match Control-Button of the Next-Segment for Position and Velocity are active.