Click on the A/B test you want to track Heatmap data on and then click Edit A/B test.
1. In the editor now click Settings
2. Click Heatmaps
3. Click Create Heatmap for project variations.
4. If you want to set up another for this test click New Heatmap otherwise close this popup by clicking the x. 
5. Go back to the dashboard and click on Heatmaps
6. Find your heatmap and click it.
7. Click Configure heatmap
Edit Audience: Audience is already inherited from the A/B test so there is no need to edit that.
Visitor Limit: If you like you can set a higher Visitor limit than the default (5000). This is however seldom needed.
Sampling: If you have a lot of traffic on your website and want to collect data over a longer period of time you can lower the sampling size so that not all visitors are registering heatmap data.
8. Show heatmap on URL: Set the URL to the page that you want your heatmap to be presented on. It is important that this page matches your Audience. In other words, if you have an Audience that will collect heatmap data on multiple pages of the same type, let's say Product Detail Pages, then you want to set the URL to a specific PDP so that all your collected data from all your PDPs are presented on this specific PDP.
9. Click Save and close and you are done!