Plesk has a lot of great built-in features for managing your database and those are often covered by guides (like this!) in great detail. User management, however, is often neglected from the limelight despite its importance.
First, log in to Plesk. Once you’re in, click “Databases” in the right sidebar and then click on “User Management” in the right sidebar on the next page.
You’ll be presented with a list of your DB users and their associated databases. Click on the one you wish to edit. Here you’ll be given the option to change the username, password, database, and the permissions to grant to the user.
Make the changes you want and click OK or Apply to save.