html for edit-author has been correctly set up.

Deokhyun_Lee_reading/bookshelf/templates/authors/add-author.html

 {% extends 'base.html'%}
-
 {% block title %}
 Add New Author
 {% endblock %}

Deokhyun_Lee_reading/bookshelf/templates/authors/author_details.html

@@ -16,6 +16,7 @@
     {{author.nationality}}<br>
     {{author.bio}}<br>
 </ul>
+<li ><button type="button" onclick="window.location.href='/authors/{{author.pk}}/edit'">Edit Author</button></li>
 <h3>Books by {{author.first_name}} {{author.last_name}} I love: </h3>
 {% if books %}
 <ul>

Deokhyun_Lee_reading/bookshelf/templates/authors/edit-author.html

+{% extends 'base.html'%}
+{% block title %}
+Add New Author
+{% endblock %}
+{% block content %}
+    <form method="post">
+        {% csrf_token %}
+        {{ form.as_p }}
+        <button type="submit">Save Changes</button>
+  </form>
+{% endblock %}
\ No newline at end of file

Deokhyun_Lee_reading/bookshelf/templates/books/book_details.html

@@ -23,7 +23,7 @@
         <p>No Available Books.</p>
     {% endif %}
     <ul>
-    <li ><button type="button" onclick="window.location.href='/books/{{book.pk}}/edit'">Edit Books</button></li>
+    <li ><button type="button" onclick="window.location.href='/books/{{book.pk}}/edit'">Edit Book</button></li>
     <li><a href="/home">Home</a>&nbsp&nbsp&nbsp&nbsp&nbsp<a href="/books">Books</a>&nbsp&nbsp&nbsp&nbsp&nbsp<a href="/authors">Authors</a></li>
 </ul>
 {% endblock %}
\ No newline at end of file