There are several ways to get to the Author environment for theory pages:
In the Author environment, click on the Theory tab. Select a theory page by clicking on its name, or by clicking on the pencil icon to its right. If the pencil is not available, you probably don't have edit rights in the author group. You can always use the search bar to search for theory pages by name or by ID number.
2. Is the theory page you want to edit already available in one of your classes? Find the theory page you want to edit on the homepage (which shows your current course). Select Edit in the three vertical dots menu (or 'kebab' menu) to its left. You can also view the theory page by selecting it on the homepage and then clicking on the Edit button in the top-left of the screen to edit.
3. You can also open the theory page in edit mode via the right-click menu of the item in the Edit chapter or Edit subchapter page.
Editing a theory page
You will now see a top menu similar to:
This means you can start editing the theory page. Make your modifications as desired. For more information about what you can do while editing a theory page, see this page on creating a new theory page.