Trigger "jump to previous" not an option

I'm kind of new to storyline 2, having spent years using Captivate, so please bear with me.

I need to make my project accessible by keyboard only. I have not been able to find "jump to previous" as an option in the dropdown when accessed from player triggers.

I successfully created keyboard navigation trigger for "jump to next" slide by pressing ], but "jump to previous" does not appear in the dropdown. My only choices are "jump to next" and then all the specific slides I have already created. I tried copying the default "Jump to previous slide" trigger and then editing it, but it requires an object be assigned to it. Why didn't it make me assign an object for the "jump to next" shortcut, which was ]

I guess I could create an invisible object on every slide, but then I'd have to perform that creation, cut paste to every slide, then make sure it's in the proper place in the tab order . . . a bunch of work just to make a keyboard shortcut for "jump to previous". I must be missing something.

(I had to use the weird square brackets for keyboard navigation as they are the few not already used by the JAWS screen reader.)

BTW, I'm not trying to create a "Jump to previous" trigger on the first slide; obviously there would be nothing to jump to!

Thanks to anyone who can help!