When you have a page without translation, you create a new translation by clicking the + in the page list table or by clicking "add new" in the language metabox in "edit page"
Since you have already written a page and its translation, you can link them by:
1. finding the id of one page (when you edit a page, you are directed on a new url : yoursite/wp-admin/post.php?post=15&action=edit. Here 15 is the id of the page you are editing.
2. Edit the translation, enter the id in the page id field in the languages metabox. Click on update.