I find that is totally impossible to change cards from “field” to hand, or sell directly from hand. Tried several times, different ways but, in the end, it is not allow to move a card from hand to Bob, or swap cards from field/hand.
As tutorial said nothing about this, and seems logic to do so, I understand that it is a bug. Maybe is part of the strategy, but then I appreciate leave this point clear in the tutorial.
Cheers.
This is by design.
I have not played the tutorial in a long time but I believe that all valid moves are mentioned and explained. The tutorial does not show which moves are invalid.