Hahah, so it was a really small plant - that’s why I just broke off one of the babies from my houseplant (and also why the ones I bought at the store in 2.5” pots were too big). I think with an opening this small you’d need to either plant some seeds, or find a tiny plant baby from a larger plant like I did.

I used a funnel to add in the rocks and dirt. And a long fondue fork to poke around and move things. :)