If you get a page featuring the message “Error Establishing Database Connection,” this means that there is a problem with the connection to your database and there could be a number of reasons for this.
This isn’t a problem that can be solved in the WordPress app (or by the WordPress app support team). You can find troubleshooting tips on the Common WordPress Errors support page.
For additional help, please contact your website hosting provider. You can also get more help and advice from the WordPress community: https://wordpress.org/support/