Not sure if it's working

It sounds like the plugin is working, then. There are plenty of ways to increase the load time of your page, and if your javascript is light-weight or set up on a cdn it might not make a difference to put it in the footer.

For more on page times, with a bit about placing scripts in the footer, see this article: https://yoast.com/reduce-http-requests-wordpress/ It may not change the actual load time, but it will change the perceived load time – that is, it loads your site’s content first and scripts second, instead of waiting to load the scripts and then the content.