How do I search for a comment I made on a Facebook group wall post a long time ago?
Follow the steps given below:
Visit your Facebook Timeline:
Click on "Activity Log". Here is a screenshot to make it easier for you to find it:
Scroll down to your heart's content until you think that you have scrolled down enough.
Press Ctrl + F on your Keyboard.
Type the keyword you want to search for.
P.S: The activity log is only available with Timeline and not otherwise. If you no longer have access to the posts of the particular group (group admin blocked you from group; it's a closed group and you are no longer a member); then you will not be able to view/delete the comment.