Everyone makes mistakes sometimes—or needs to make important additions or updates. You can make changes to any message that you've posted to Yammer, no matter what type of message it is or content it contains.
Find your post that you want to edit.
At the bottom of the post, click Edit.
Edit is only available on your own posts.
Tip: To delete a post, select the More icon , and then click Delete.
Make the changes that you want to your message and click Save.
Edited appears at the top of the message.
Anyone who can see a message can see any previous versions:
At the top of the message, click Edited.
An Edit History box with previous versions appears.
Click the X in the upper-right corner to dismiss the Edit History box.
Editing a post is not available for Yammer external groups.
The ability to change attachments (files and images) is not currently supported.