PHPMyAdmin is telling you that your MySQL service is missing a root password. You can change it by accessing the MySQL command line interface. mysqladmin -u root password newpass
Here the simple step that you can easily set phpMyAdmin Password.
Goto C:\xampp\phpMyAdmin and find config.inc.php file
Open config.inc.php file in Text editor like Notepad++.
Find the line $cfg['Servers'][$a]['auth_type'] = 'config'; in config.inc.php file.
Change the word $cfg['Servers'][$a]['auth_type'] = 'config'; to $cfg['Servers'][$a]['auth_type'] = 'cookie'; in config.inc.php file and Save the changes.
Now open browser and type localhost/phpmyadmin. Enter username is root. password is null means empty. you don't type anything leave blank and press GO button.
Now you can see change password link. please click that link.
Set your phpMyAdmin password and retype again and press GO button.
I just faced the mysql user password problem - ERROR 1045: Access denied for user: 'root@localhost' (Using password: NO) - when I tried to do a do-release-upgrade on my operational system. So I corrected it in 2 steps.
Secondly, with one of the users that I know the password, I made some password changes to the others users through phpmyadmin itself according to SonDang's information.
On linux (debian 9) after resetting the mysql(Maria DB) root password, you just have to edit the phpmyadmin db config file located at /etc/phpmyadmin/config-db.php
If you tried mysqladmin -u root password 'your_password' and MySQL says denied access, you need to change the my.ini so that the value password is blank. then try mysqladmin -u root password 'your_password' again. It should change your password and open my.ini again and change the value password to the previous one.