Welcome to Android Central.
There are so many questions.
Where did you get this device where something could have been missing or removed?
Why is return not an option, besides voiding any warrantee by opening the device? I mean it isn't like you've had the device for months and suddenly the sound stopped if a part was missing?
Speaking of missing parts, have you watched a teardown video or something to know for sure this piece is missing? Is it possible that this part is used in different applications and in this one, that empty plug is supposed to be empty?
It would be helpful if you posted a photo of what you're seeing so we are all on the same page. You would have to use an external device to photograph the components and then post the images as screenshots. It would help us if we had more information including a screenshot. This link will help you show us that…
Truthfully the way I see it, if you have the part number and are not able to find the part your alternatives are limited to exchanging the device for one that works, if you still can, buying a parts only device and scavenge the needed part or replacement. Well you could just live with it too, but a phone without sound is like a building without a door, sure it works it just isn't very useful.