Like for answer we can edit them. But what should we mention there? And comment can't even be edited. So what should be done for this?
For comments flag as
Obsolete or use
Other and briefly describe what is wrong with that comment.
if you gained edit privileges try to find a working replacement link - if you can't find one consider editing and removing the link + add what you've done to the edit summary.
if you do not have edit privileges - suggest an edit ( if you can find a working link) or flag for moderators attention and explain what is wrong.