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Stop MySQL:
systemctl stop mysqld

Set the mySQL environment option
systemctl set-environment MYSQLD_OPTS="--skip-grant-tables"

Start MySQL using the options you just set
systemctl start mysqld

Login as root without a password
mysql -u root

ALTER USER 'root'@'localhost' IDENTIFIED BY 'MyNewPass';

Stop MySQL
systemctl stop mysqld

Unset the MySQL environment option so it starts normally next time
systemctl unset-environment MYSQLD_OPTS

Start MySQL normally:
systemctl start mysqld

Try to login using your new password:
mysql -u root -p