Thanks for your response, but I'm not finding any option like that, either.
Here's a little more detail on the context of my specific problem:
This morning, for no apparent reason, my 4 month old iPad Air decided it would not turn on. I plugged it into my PC and iTunes was able to access its contents, or at least some of it; it's not really clear.
One of the options for dealing with this situation, according to the Apple support page I read, is to have iTunes reset the iPad, which is misleadingly called "Restore iPad ...". (Evidently, this condition is common enough that there is a separate page for dealing with it.)
After backing up the iPad to my computer using iTunes, I started the so-called "Restore" process, only to be told that "There are purchased items on the iPad ... that have not been transferred to your iTunes library. If you restore this iPad, these items will be erased and you will have to purchase them again. Are you sure you want to continue?"
Naturally, this message does not give me an option button to "transfer" the purchased items to my "iTunes library"; in fact, the message does not even give the slightest hint as to how such as "transfer" might be accomplished. It also does not give any clue as to what has not been "transferred to [my] iTunes library."
So far as I can tell, the only thing that I have purchased that has not been downloaded to my computer are my iPad apps. Do I have to download those to my computer? That seems idiotic, but, then again, I am new to the Appleverse and am not familiar with its arcane and recondite ways. All that I had ever heard was that Apple stuff was supposed to be intuitive and easy to use. This seems to be the exact opposite.