The Cast icon should be located at the top right of the Promota app.

If it is not there, make sure you have done the following steps:
Chromecast is set up properly.
Chromecast is plugged into the display and powered on.
Chromecast is connected to the same wifi network as your phone.
Your phone is connected to your store's wifi network.
Once you've done the following, the Cast icon should appear at the top right of the app.
For detailed instructions on how to setup Chromecast, please click here.
For detailed instructions on how to cast to Chromecast, please click here.