Once a respondent submits a survey response, they cannot return through the survey link to modify their answers, even if the survey is updated afterward. Any new or modified questions added to the survey will only be visible to respondents who take the survey after the update.

If you need to include responses for a newly added question for participants who have already completed the survey, you can manually update the response data as a survey owner.

Steps to manually update a response:

Navigate to Analytics → Response Viewer.

Locate and open the completed response you want to update.

Click on Response ID

Click Edit Response in pop up window.

Enter the response for the newly added question.

Save the updated response.

Help file for reference: https://www.questionpro.com/help/response-viewer.html