real-time data(push dataset) using custom visualization on the dashboard

I would like to display real-time data (Push dataset) using custom visualization on the dashboard.
With Q & A on the dashboard that references the Push Dataset, Built-in visualization is available.
However, when I click [Import a custom visual], nothing is displayed (the import dialog is not displayed).

operation procedure in Power BI(web).
(1)Open a dashboard references a Push dataset.
(2)Click the text box [Ask a question about your data].
(3)Entry any word.
(4)Click [VISUALIZATIONS pane -> Import a custom visual -> Import from file]
->nothing is displayed

Is this a specification, or is it a problem?
Please tell me how to do it.