Resetting the MySQL root password in CentOS 7 is straight-forward.
sudo systemctl stop mysqld
sudo mysqld_safe --skip-grant-tables &
After the server has started, and if looks like it is hanging, press enter and the command prompt should become available again.
use mysql; update user set authentication_string=PASSWORD("mypassword") where User='root'; flush privileges; quit
sudo systemctl stop mysqld sudo systemctl start mysqld
mysql -uroot -p
You should now be able to use your new password.