That seems odd to me as well, I'm not 100% sure to be honest with you. I did Google around for a button but I couldn't find what it would be.
However, a user on another forum said
you could try this, if it doesn't work, it's possible there is no button.
Again, I don't have the keyboard, so I'm just Googling around and am not 100% sure, but this is just the way it's looking.