I have installed and activated the ClickHeat plugin in Piwik. But I can't see any heatmap data in Piwik dashboard.
Please see the below images.
The Plugin you are using is a third-party plugin and therefore not supported by the piwik team. According to this github issue the plugin isn't compatible with Piwik 3.
As it seems like the plugin isn't maintained any more, I'd recommend you to look into the official heatmap plugin, which does the same and even more.