You can execute the RENAME USER statement to modify the name of an account.
Syntax
RENAME USER old_user TO new_user
[, old_user TO new_user] ... Example
RENAME USER account2 TO account_2;
SELECT User, Host, Password FROM mysql.user;
+----------+-----+----------------------- -+
| User | Host| Password |
+----------+-----+-------------------------+
| account2 | % | *61f3777f02386598cda****|
| account_2| % | *0fe79c07e168cabc99b****|