This filter can be used to change the value displayed inside of the summary magic tag for a specific field.
This filter was added in Caldera Forms 1.5.0.10
Change How A Field Value Is Shown In Caldera Forms Email Using Summary Magic Tag
Where Does This Code Go?
When using WordPress hooks to customize Caldera Forms or other plugins you should not modify the plugin files, or you will lose your changes when you update the plugin. Instead you should create a small plugin to hold the custom code. It's easy, learn how here.
Technically you can add the custom code to your theme's functions.php, but then you will not be able to change your theme and keep these customizations.