Henka Wasa is a basic part of Aikido. It is the art of changing from one technique to another technique. For the test the instructor calls out a technique to start with and the student then has to start that technique and then change to other techniques. In Randori Uke might counter the first technique so Nage has to change techniques or Nage might change techniques because of other attackers, the layout of the room, Uke's safety, or just for fun.
The approach taken here is to go from a technique back to the basic movements of Arm Up or Arm Down. From either of these one can change to the other and to any technique. For this reason all one needs is to know is how to get back from the technique to the basic arm positions. There are usually numerous ways to do this but as usual a simple systematic approach will be taken here.