Well, it’s not like the idea of “transpose” is new: we have used that in numpy all over the place in DLS C1 and C2 already. So you know the concept, now all you have to do is figure out how to implement that in TensorFlow. I can name that google search in one guess! 
I grant you that they have gone out of their way to condition us to expect very solicitous hand-holding in the courses thus far, so perhaps this does constitute a legitimate violation of your expectations. But as we arrive in the land of TensorFlow the waters are pretty deep and perhaps they feel that it’s time to encourage us to develop our own “swimming muscles” a bit more! 
But seriously, it will be necessary to spend some time with the TF documentation and tutorials and also the forums as we get to Course 4 and Course 5 and get more seriously into the use of TensorFlow. There are also lots of very helpful threads on the Forum, e.g. this one (which is not relevant here in DLS C2 W3, but will be very useful when you hit DLS C4 W1 A2).