To change the “Proudly Powered By WordPress” on Twenty Seventeen them the first thing you’ll need to do is to create and activate a child theme (hint: if you want the really easy button, just go download the pre-built child theme).
Once you’ve created and activated your child theme, copy the footer.php file over from Twenty Seventeen into your child theme directory. Next, open up footer.php and look for this bit of code:
get_template_part( ‘template-parts/footer/site’, ‘info’ );
Now you have a couple of options. You can simply comment out that line by adding // just before the code, or you could consider replacing it with your own custom footer text. Here’s the code I added to create the footer text you see in the image above: