If you will edit your comment, there will be a remark just below the comment to show other people that the comment was edited.
Follow these steps to edit comments
Step 1: Go to the post where you had made the comment and take mouse over the top-right coroner of the comment. You will see a pencil icon to Edit and Delete the comment.
Step 2: Click on this icon and select Edit. If you want to delete the comment permanently, click on delete icon.
Step 3: Now you will be able to edit the comment. Edit the comment and then press enter to post it again.
You will also see that Facebook has remarked this post as edited after your finish editing.
When you will click on this link labelled as “Edited,” you will see the edit history that will allow you to see the original comment and all its edited form. This “Edited” label will be visible to all Facebook users who are allowed to see the posts and comments.