[Wendy Cutler]

OK, wait. The 10th time I tried this, I thought I was just exiting and clicked the tablet device back button. That brought up the list of my Dropbox folders, still with the Add [filename] to at the top. 
Uh. Okay. I guess I have this. Yep, tried that again. That's how that works. 
Really, I was looking for a button or something in the software to Change the folder. As I said, clicking the device back button for me meant that I was giving up.