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If you are an Organisation Admin, you can edit any story within your organisation
Posts, Updates and Survey Responses are all Stories.
Steps
From the Timeline or Newsfeed
Press the cog symbol that appears in the top right corner of the story
A dropdown menu appears
Select the Edit option
You arrive on the Edit Story page in Several or No Contacts view which means that a table will be displayed showing a row for each of the contacts (or survey respondents) in your project. You might need to scroll down through the table to find the row for the contact or survey respondent whose response you want to edit.
Make changes to your story and then scroll to the bottom and press Publish Now
From the Story page
Go to the Story page of the story you want to edit
Press the More Options button on the right
Select Edit Update
You arrive on the Edit Story page
Make the changes you need to make
Scroll to the bottom and click Publish
