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/