Log into mysql
mysql -u root -p123456

After logging into MySQL, execute the following commands one by one:
MySQL>use mysql;
MySQL>GRANT ALL PRIVILEGES ON *.* TO 'root'@'%' IDENTIFIED BY '123456' WITH GRANT OPTION ;
MySQL>FLUSH PRIVILEGES;
Log into mysql
mysql -u root -p123456

MySQL>use mysql;
MySQL>GRANT ALL PRIVILEGES ON *.* TO 'root'@'%' IDENTIFIED BY '123456' WITH GRANT OPTION ;
MySQL>FLUSH PRIVILEGES;