Time Machine - Change Disk Button?

I just posted a question regarding Time Machine, here in this forum. I tried to add to it but it kept getting rejected, so I am asking the added question here:

By the way, I'm going in circles trying to find out what people mean when they refer to the "star wars" symbol, button or icon. It's amazing that no matter how I word it, all my search result assume I already know what and where it is, and rather than explain it, go on talking about all other things in Time Machine. And I have followed numerous links, suggestions, troubleshooting guides, etc. Nothing tells me what this is.

Nor, for that matter, can I find out why, "Change Disk" is nowhere to be found in my Time Machine preferences, yet when I search for that, I get all sorts of tips on all sorts of related things. I only have "Select Disk."

Anyone? Thanks.