Hello and thank you Mr Carl for your answer!
i found the button and i press it but it shows me a white screen and
writes in a box :
We're sorry, but something went wrong.
We've been notified about this issue and we'll take a look at it shortly.
I am sorry. There should be some recent code changes broken this feature. We will fix it. Thanks your patience.
When I visit your product page, the preview images are shown as broken, they are unavailable . Combined with log analysis, it's the root cause. Have you seen them correctly before? I have deleted the database record for your preview images. Now you should be able to click "Change Request" icon, check "Make public" option, and upload your preview images again, then click "Submit Request" button.