Unfortunately it is not possible to add user defined filters with Newsstand reports. The report is already generated once it reaches the Newsstand. Filters cannot be applied from there as a result.
Newsstand is a 'destination' that can be configured in the NPrinting publish task. Filters for newsstand reports need to be configured in the publish task or directly on the NP report in the NP web console.
If you need to apply specific filters 'On Demand', I suggest leveraging On Demand for Qlik View and or Qlik Sense.