It is possible to Edit/Delete a continuous feedback which you have posted for 15 minutes after posting it.
Once you have posted your feedback, it will be available on the wall with options to Edit/Delete for the next 15 minutes. After the feedback is published edit/delete is not allowed.
If you want to Edit/Delete the post after 15 minutes, please contact HR.
PS: Synergita implementation for your Organization may vary from how the features are described here. The screen shots given here may also be different from what you see in your system. Please talk to the concerned person in the Organization for any specific queries.