This could be a developer question, if this is an app that uses a AVPlayer or WKWebView component. It's not impossible that the video player view is laid out in Interface Builder so that it looks like it's going to extend to all the edges of the screen, but to actually be smaller at run time.
Also, there isn't really a gray frame around the player. There are horizontal dark-gray areas above and below, which look like window background, and vertical black areas on the left and right, which look a fill provided by the video player view itself, where the view height and aspect ratio force the width to be less that the full view width.
As far as the top and bottom are concerned, this looks like there are incorrect auto-layout constraints, and/or incorrect view controller configuration. The thinner gray bar at the bottom looks like the default distance for a constraint from the video view to its superview. The thicker gray bar at the top looks like a constraint from the video view to a safe area (maybe), or maybe there's a full-height navigation bar that simply has no text up there.
A good way to start debugging problems like this is to use the view hierarchy debugger in Xcode (on the debugger toolbar when you pause execution). You can "tilt" the debugger view to one side to see where are the views are, which narrows down which part of the code you have to look into.
So, the answer to the question "Who can I contact that can remove the gray frame…?" is probably: "You are the person who can fix it, with a bit more debugging work." 😀