You can always add or change something in any material, even after it has been published.

Basically, you edit it in the same way as you do before publishing. To edit a press release, you go to Press releases, then click on the title of the material you want to edit (or click on the three dots menu and choose Edit). 

The moment you click the blue button Save and continue to distribution to confirm your changes, the web version of the material will be updated.

No distribution emails or alerts will be sent out when updating an already published material, since distribution is only available the “first” time that you publish. In the case that you want to add further distribution to the published content, please see our information about how to send already published content to more recipients.

Emails that have already been sent out with the material, will naturally not be updated, but when a recipient clicks in the email in order to display the material on their browser, they will see the updated web version.

Also, if the material already has been shared on social media, it might require a debug on the social media site in order to refresh the presentation of the material in the social media post.

Please also see:
How to publish a press release, news or blog post
How to send already published content to more recipients
Facebook and LinkedIn show an old version, although I updated the material on Mynewsdesk.
In which cases are emails being sent with the content I publish?