Go to the terminal

sudo apt-get install mysql-server mysql-client libmysqlclient-dev

• libmysqlclient-dev allows you to compile useful plugins for mysql use.

As there is no password set for root user, simply login with blank password

sudo mysql -u root -p
Enter password: (press enter as no password is set)

after then can easily run query

ALTER USER 'root'@'locahost' IDENTIFIED BY '<password>';