You will need to install a user script manager extension to install this script.
Just navigate to your profile while logged in, and Reddit History Sanitizer will start looking for old comments. You'll have to switch it off if you're just trying to browse your old comments though.
This was created after use of Reddit Secure Delete - Only Comments More Than 7 Days Old, and is meant to be an improvement on that based on my own expectations of the script. Mainly, I wanted it to continue searching for comments beyond just the first page. I also chose not to use the unsafeWindow object, which I think makes it a bit more secure.