Watch this video for a step by step process on How to Modify Database User Privileges in Plesk Panel
Privileges grant users the ability to change and manage databases. You can reassign or modify the Maria DB database user privileges with Plesk.
To Modify Database User Privileges
1. Log in to your Plesk.
2. Select Databases from the navigation menu.
All the operational databases in your Plesk account and related options will appear.
3. Click on User Management.
A list of active database users will show up.
4. Click on the name of the database user to change its privileges.
A form with customization settings for the user account is displayed.
Scroll down and, you will spot the Privileges section divided as Data Access and Structure Access.
5. Select the privileges you want to grant the user and click the OK button at the end form.
That is all it takes to grant user privileges to a database in Plesk.