Solution 1

UPDATE mysql.user SET Host='%' WHERE Host='localhost' AND User='username'; UPDATE mysql.db SET Host='%' WHERE Host='localhost' AND User='username'; FLUSH PRIVILEGES;

Solution 2

Best answer on Stackoverflow suggesting to use RENAME USER which copy the user privileges.

Using Data Control Language (statements as GRANT, REVOKE, RENAME and so on) does not require FLUSH PRIVILEGES; and is required in architecture like Galera or Group Replication in MySQL versions having MyISAM tables in mysql database because MyISAM tables are not replicated.