Sony Reassembling my rx100m3, Don't know what this piece is

[Fluke]

Hi guys, my friend dropped my rx100m3 down rock faces down into a lake and I quickly picked it up within 20 seconds. I took apart my rx100 to a certain point (not that far just took apart the LCD back to see how much water was inside) I was following a video on youtube, and a black piece of plastic fell off. My question is that I don't know where this piece goes and I want to reassemble it and leave it in the rice for a month. Any help would be much appreciated since this camera means a lot to me. Thanks

PS I was following this video :

 

[NoSeconds]

Just turf it, there's no such thing as a good repair job without spare parts left over...