Finish the video message.
Drag the cursor on to the picture.
At the bottom left cornerclick the pause button.
Then it will show you the video message.
this option is just to make us fool , but reality is that ,those message are undeleteable because whenever you open your id on another device , they will apear again like a devil ugh, i am fed up, why i can delete a video message if i sent it by mistae........