How to rename MySQL database user in Plesk?
You can change the existing Mysql database username following the steps given below.
Step 1: Login to Plesk control panel.
Step 2: Under Databases, click User Management.
Step 3: Click on the required username to be changed.
Step 4: Provide the new name in the Database user name field and click OK.You can also change your password, roles and privileges here.
Respective username and other changes will be changed as shown in the below image.