Consider this instant in the technique: Nage has a proper grip on Nage’s wrist and elbow, and Uke‘s arm is slightly bent and rolled forward with Nage being slightly behind Uke and about to rotate Uke down.

For the test, the committee wants to see you extend Uke‘s arm a bit forward then draw a generous spiral to the ground behind Uke.

As a variation, if Uke has locked his elbow, or you are thinking to yourself “why not?”, you can simply extend Uke‘s arm and slightly behind him in the direction of his shikaku, or dead angle. He will naturally start to fall backwards and you can continue the ura technique from here as well.