Hi!
The part you are having is the hinge. This is required for opening and closing the 3DS.
Here you can find the part: https://www.aliexpress.us/item/2251832520249568.html?pdp_npi=4%40dis%21EUR%211.53%211.32%21%21%211.66%211.43%21%4021014bee17273454698375001d1401%2112000029002771688%21affd%21%21%21&dp=0678f250adaf17fbd558cfaaa6188db4ad9d8d3e&aff_fcid=cd61cb79e1c641edb217b91e421abff8-1730096813018-01530&aff_fsk=&aff_platform=api-new-product-query&sk=&aff_trace_key=cd61cb79e1c641edb217b91e421abff8-1730096813018-01530&terminal_id=3e725264d80e4df19584ff420276478c&afSmartRedirect=y&gatewayAdapt=glo2usa4itemAdapt
Regarding the last photo, I think that the LED diffuser and the hinge lock goes there! You can find those parts here: https://www.amazon.com/Gametown-Nintendo-Replacement-Middle-Diffuser/dp/B00YAFPRA4
If you have any more questions, please let us know!