Major Problem of Mi 4A 40 Inch TV

I bought this Mi TV 4A 40 Inch Full HD from Mi Home Acropolis Mall, Kolkata today while playing some videos i can see that it not playing in full screen. While searching for changing the aspect ratio on Setting but sad part i cannot find it. Played some videos on VLC Player where it has in-build feature to change the aspect ratio but still its not plying in Full-HD. Played some videos on
some different app but same problem persisted. Mi should fix this major issue.

Mi,Mi TV,Mi TV 4A,Mi 40 inch Tv,