Modifies one or more characteristics of an existing event.
 
Syntax
------ 
ALTER
 [DEFINER = { user | CURRENT_USER }]
 EVENT event_name
 [ON SCHEDULE schedule]
 [ON COMPLETION [NOT] PRESERVE]
 [RENAME TO new_event_name]
 [ENABLE | DISABLE | DISABLE ON SLAVE]
 [COMMENT 'comment']
 [DO sql_statement]
 
Description
----------- 
The ALTER EVENT statement is used to change one or more of
the
characteristics of an existing event without the need to
drop and recreate it.
The syntax for each of the DEFINER, ON SCHEDULE, ON
COMPLETION,
COMMENT, ENABLE / DISABLE, and DO clauses is exactly the
same as when used with CREATE EVENT.
 
This statement requires the EVENT privilege.
When a user executes a successful ALTER EVENT statement,
that user becomes
the definer for the affected event.
 
(In MySQL 5.1.11 and earlier, an event could be altered only
by its definer, or
by a user having the SUPER privilege.)
 
ALTER EVENT works only with an existing event:
 
ALTER EVENT no_such_event ON SCHEDULE EVERY '2:3'
DAY_HOUR;
ERROR 1539 (HY000): Unknown event 'no_such_event'
 
Examples
-------- 
ALTER EVENT myevent 
 ON SCHEDULE AT CURRENT_TIMESTAMP + INTERVAL 2 HOUR 
 DO 
 UPDATE myschema.mytable SET mycol = mycol + 1;
 


URL: https://mariadb.com/kb/en/alter-event/