1)Login to Plesk control panel.

2)Click on Subscriptions.

3)Click on subscription name.

4)Click on Database tab.

5)Click on User Management .

6)Here you can find the list of the user, select the user which you want to remove then click on Remove

7) Click on Yes if you want to remove the user and No if you not want to remve the user.

8)Here you can see the information that The selected database users were removed.