1) You can use the getData method on the BackendApi to fetch additional pages of data.
getData method ‒ Qlik Sense
2) You can use the Field API to select a data point in the app which will filter the underlying data model and refresh all objects and data cubes. This will also trigger a re-validation of your object.
selectValues method ‒ Qlik Sense
2.5) If you don't want to filter the entire data model you probably want to incorporate Set Analysis in your expression.
This is a intro video Set analysis – an introduction ‒ Qlik Sense