Use a dedicated media player (VLC, MPV) or embed the MKV in an HTML5 player that supports transcoding.
The string "http- myserver.com file.mkv" is invalid for any computing or networking purpose. A functional essay on this topic would break down its three distinct errors: http- myserver.com file.mkv
location ~ \.mkv$ add_header Accept-Ranges bytes; add_header Content-Disposition 'inline; filename="$1"'; mp4; # Note: Nginx's ngx_http_mp4_module works best with MP4; for MKV, rely on range. Use a dedicated media player (VLC, MPV) or