This Update was published Sept 9, 2021. This is possibly a better method to insert a copyright notice or other site information into the footer of your Twenty-Seventeen WordPress Theme.  First, search for and install the plugin known as “Options for Twenty-Seventeen.” Then, in the WordPress Administrator’s Dashboard, go to “Appearance,” select “Widgets,” and insert (drag) a “Text” widget into the “Site Info” widget area.  There is no need to insert a title to the text widget.  Just insert the copyright notice or other desired text into the Text widget that you want to appear in the Site Info area of the footer of each page of your website. Click “Done” when finished adding text in the Text Widget.

Following is this article as originally published on 03-18-2017:

In the WordPress Admininstrator’s dashboard, select >Appearance, select >Editor, and select >footer.php from the list on the right margin.

Edit the footer.php file.

Locate this part of the footer.php file:

get_template_part( ‘template-parts/footer/site’, ‘info’ );
?>
</div><!– .wrap –>

Change that part as follows:

Insert “//” at the beginning of the “get_template_part” line in order to comment-out this line. Next, insert the 4 lines shown below between the “?>” line and the </div><!– .wrap –> line.

//get_template_part( ‘template-parts/footer/site’, ‘info’ );
?>
<div class=”site-info”>
<a href=”https://wordpress.org/”>Copyright 2017, Your site name</a>
</div>
</div><!– .wrap –>

Customize by fixing the URL — http://www.yoursitedomain.com/  and Your site name.

Save your changes / update / the footer.php file.

Note:  Your modifications will likely be overwritten in the next WordPress version update.  That’s okay.  And, it might be easier to again edit the footer.php after the version update rather than trying to figure out how to use a child theme that would preserve your modifications from being overwritten due to a version update.