Is there any specific format to edit the post? I have checked multiple modified answer some people mention Edit and add the edit comment.
From my experience there doesn't seem to be a specific format and its up to the judgment of the user. If the edit applies to the original post being edited than I believe it makes sense to clearly state the edit and a brief explanation as too why. This way people coming to the site/question can more easily see the relevant information and they won't need to scroll through multiple comments. Edit should be used to make the relevant information easier to find in my opinion.
In my opinion purpose of edit should be to make post more easier to read and understand, without harming the post. After edit the intent of post should be same as before.
One should not edit any post to add his/her comment or answer to the post.
To make post more easier you can correct it grammatically, also if added code is having very bad formatting you can improve that in edit. You can add relevant tags which helps to define the topic.
An edit made to just highlight some text is not required.