How to add media conversion to existing media instance

Question

I have my existing $media instance and I would like to generate a thumbnail at $seconds. I tried:

$media->manipulations = [
  'thumb' => [
    'height' => '250',
    'extractVideoFrameAtSecond' => $seconds,
  ],
];

$media->save();

But get this error:

Can not convert image. Unknown operation extractVideoFrameAtSecond used