how to edit an old post?

Dear Moderators,
Is there some way that I or you can edit a certain post that occured a couple months back? A client had contacted me and said they did a goodle search for their url and found one mentioned on this forum– I had included their url in a post that asked for help. They’re not comfortable with it and I tried to edit it but I guess it doesn’t allow me to do so.

Sorry for the inconvenience about this.