I currently have a freeform which allows a user to register his/her information. I'm looking to build an edit page for each of these entry's so the user can come back and edit it if they've made a mistake.
I don't know of a native way to edit Freeform submissions on the frontend, at the moment. Apparently Freeform 3 is coming out next week and it includes front end submission editing! Based on this edition comparison page it will only be available for Freeform Pro.
I did think of a way to accomplish this right now.
Setup an Element Connection for the form you wish to allow editing for. Make the connection to a new Craft section (e.g. User Submissions). Then you can use a standard Craft edit entry form to allow your users to make edits. When creating the Element Connection make sure you pass some sort of Craft user identification so the new entry is tied to the correct Craft user. That will make editing much safer and easier. The downside to this method is that Freeform will no longer hold the master version of the submission. That would limit your ability to use some of Freeform's features.