Update my Wordpress plugin to place script before closing body tag rather than header

I have a Wordpress plugin, available on Wordpress and related to a SaaS product, that helps the user install a required script on their Wordpress site. However, I want the script to be placed prior to the closing body tag, rather than in the header tags which is how the plugin works now. So I need the existing plugin files adjusting so that the script the user enters into the text area on the plugin settings page is placed before the closing body tag on every page, and not within the header tags. Additional code that doesn't support this also needs to be removed from the plugin to clean it up (there's quite a bit of unnecessary code relating to the header for example). So it needs to be cleaned up, streamlined, and ensures the script entered by the user goes before the closing body tag, not within the header tags.