If you click the spanner icon you can add different statistics to the report and then select them for the visualizer. If the type of fold statistic you want is not available then you will need to use a custom statistic - there are some available in the
Download Warehouse or you can create your own.
This guide covers the basics on custom statistics creation and
this guide goes into more detail. While the latter was written for PokerTracker 3 and the user interface is different the techniques still apply to PokerTracker 4.