Make sure you have Stopped MySQL first (above).
Run the server in safe mode with privilege bypass: sudo mysqld_safe --skip-grant-tables
mysql -u root
UPDATE mysql.user SET authentication_string=null WHERE User='root';
FLUSH PRIVILEGES;
exit;
Then
mysql -u root
ALTER USER 'root'@'localhost' IDENTIFIED WITH caching_sha2_password BY 'yourpasswd';

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

use mysql;
update user set authentication_string=PASSWORD("mynewpassword") where User='root';
flush privileges;
quit

-- In case the UPDATE command returns "Column 'Password' is not updatable" run
ALTER USER 'root'@'localhost' IDENTIFIED BY 'newPassword';
flush privileges;

ALTER USER 'root'@'localhost' IDENTIFIED WITH mysql_native_password BY 'root';

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

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

$ sudo apt install mysql-server
$ sudo cat /etc/mysql/debian.cnf

#****** please note that this process is unsafe and it stops once you run
# 'sudo service mysql stop'
# type this in your terminal or cmd
sudo /usr/sbin/mysqld --skip-grant-tables --skip-networking &
# then run this command
mysql -uroot

mysqladmin -u root -pType_in_your_current_password_here password ''