Hi there,
Depending on the js library you are using, you would likely need to either pass in the specific selectors when instantiating the functionality, or add specific classes to the markup.
For the former, you can use the browser tools to inspect the fields you want to apply the mask to.
For the latter, you could create a custom template and modify the markup to include the necessary classes.
For more information on working with custom templates for our plugins, check out the Themer’s Guide: https://support.theeventscalendar.com/153124-Themers-Guide
Hope that helps!
Sky