WP Website Troubleshooting

I am looking for an experienced WordPress developer to troubleshoot and fix an issue with an established WordPress website. The website was working normally but is currently showing a database connection error. The site is hosted on an IONOS VPS using Plesk. Other websites on the same server are working normally. I need someone to: Diagnose the cause of the database connection problem. Restore the website's connection to its database. Verify that the existing website and database are intact. Make sure the website is functioning normally after the fix. This is an existing website, so I do not want the site rebuilt or redesigned. This is a one-time troubleshooting job. Please have experience with WordPress, MySQL/MariaDB, and server/Plesk environments. When applying, please briefly explain how you would approach diagnosing a WordPress database connection issue.