The last control group is labeled Export Properties. The Quality drop-down menu has three optional settings. Generally, the Normal or High setting will do. Consider using Ultra only for situations involving highly detailed imagery in the overlay channel, and especially slow transition speeds.
Hint: Again, using unnecessarily high settings without a good reason simply wastes valuable Effects Memory.
To select an icon for the new transition to be generated, drag the scrub bar beneath the canvas to a suitable frame and click the Set button in the Export Properties group.