Hello,
Thank you for submitting a question about extracting a single site from multisite. There are many different ways to do it, and some of the methods involve plugins. Here is one of the ways I have found easiest:
In the WordPress admin area, under Tools, you will find an Export button. This will export all the site content to an .xml file. Then, create a new blank site that has its own database. Under Tools again, click the Import button and select WordPress Then you can import the .xml file, which contains all the site content.
Best,
Christopher M.