The “hobb” gear is the feed gear (metal) with the teeth that grip the side of the filament. It is tied to the larger black gear for a gear reduction (to give the stepper motor stronger mechanical advantage). The stepper motor has a shaft with a flatted side and there’s a smaller gear with a grub-screw that snugs this to the flat. If the black gear can spin freely even if the motor isn’t turning, I’m wondering if the grub screw wasn’t tightened down on the shaft.
As this sounds like a new printer, I don’t recommend you disassemble the print-head on your own. You may want to phone LulzBot tech support to ask for guidance.
The print-head is attached to the x-carriage with just three screws and one wire harness (this makes it pretty easy to remove) – although that’s not counting the cosmetic cover on the print-head (I think the cover is held in place with 3 screws).
If you’re interested, the document that explains how your AeroStruder print-head is assembled is located here: https://ohai.lulzbot.com/project/lulzbot-mini-2-aerostruder-assembly-and-packaging/mini-2/
BUT… don’t disassemble it … phone LulzBot support. That document is just for your reference. If it wasn’t under warranty… you could use those steps.