How do i close 2 faces with a smooth edge? Screenshot attached

I've attached a

https://preview.redd.it/8jdkgwb4d8rh1.png?width=1045&format=png&auto=webp&s=e47f75ba37adcfedf0a25c044e007d9ff5e6d7eb

I am modeling a top cover for a device and cant figure out how to close the gap between those two faces, preferable along the curve there. I am still struggling with the interface so please, explain what tools to use and what to select (face, sheet, curve and so on).