I had to press I (i) and not 1, as it says on the screen. So keyboard controls work. But I cannot get my controller to work, unfortunately.
Viewing post in Rival Ultimate Steel Hand (Prototype) comments
Why not explain that in game directly? I don't think there's any reason to use Tekken notation instead of an actual binded key (or a controller button) on that particular screen. Plus, even if the player is familiar with the notation, he still needs to know which keyboard keys are being used by default.