I have lost my password for a mysql database.
I am planning to move site/s to another server.
How to change in WHM/cpanel?

Which password have you lost? A user password for a script? If so which script?

There are ways to work around most of them but I think for anyone to help you we need a little more info.

Your hosting provider should allow access to phpMyAdmin management regardless of your individual user accounts (the host has a "master" MySQL account for each WHM/cPanel client - the password information for this account should be synched to your WHM/cPanel access).?

Have you tried resetting the password for the account in question through WHM so you may regain access through the site's cPanel?

yes just go on your msql databases scroll to the bottom and click phpmyadmin