I'm not sure about that exact window, but you can try putting your cursor in the upper left corner (among other things).
If you do and your cursor changes similar to the image below, you can just click and drag it to make it larger or smaller.
View attachment 24538
That's with Linux Mint Cinnamon. The red arrow points to the changed cursor and shows you where you need to point if you can in fact change the size of said window.
If you can't resize the window, I'd consider that fairly poor form. Within reason, you should be able to resize that sort of thing - even if it makes it difficult to use. That should be something a user can do with their windows.