Front end editing problem

I think I found the problem, but don’t know how to fix it yet.
When clicking on the EDIT button in the front end page, the generated URL looks like this http://xxxxx.net/?action=edit-todo&id=32
The system doesn’t know where to do this action. I manually edited the URL to http://xxxxx.net/?page_id=39&action=edit-todo&id=32 and the edit window opened in the same page.
Where should I edit the PHP to have this result? Please advise.
Is there a setting I missed to show to the To-Do list where is the page?
Thank you,
Ash.