Please find the below article which might be helpful.

https://community.pega.com/knowledgebase/articles/case-management/84/saving-data-data-page-part-flow

1. Configure a savable data page.

2. In the Diagram tab of a flow, click Smart shape menu icon Smart Shapes Save Data page .

3. Right-click the Save Data Page smart shape and click View Properties.

4. In the Automation details section, in the Data Page Name field, select or enter the name of the savable data page that you configure in Step 1.

   The selected or entered name must be an autopopulated property that references a savable data type.

5. Optional: 

   To specify an autopopulated property, complete the following steps:

   1. Select the Use associated property check box.

   2. In the Autopopulate Property Name field, select or enter the name of an autopopulated property.

6. Click Submit.

7. Drag the Save Data Page smart shape to the part of the flow in which you want the data in the data page to be saved.

8. Click Save.