Problem with topspin

hi...

i watched your video about doing topspin against block but i can not do it like you exactly please help me give me hints or show me some ways to improve it

Hi Mehrdad,

What is happening when you topspin the ball?

Are you making contact? Are you hitting the ball long or into the net? Are you generating spin?

Let me know and I will try to help further. The other option is to use the Analysis section of the website.  By submitting a video I will be able to see what is happening.