It is easy to select a Schema and there are a number of ways/places to do it, as shown in the video.
Note 1: The selected Schema is used for all randomisation in Wotja (W24+ Schemas are prefaced with the Feature Set number), be that for in-mix randomisation or to create an automix etc., or for generating a Flow that you then wish to export to a mix file.
Note 2: If you have a Pro OTB and select/use a Schema for a later major version of Wotja then Wotja will operate in Lite mode. See this FAQ: I have a Pro OTB but Wotja is operating in Lite mode. Why?