You can use this statement to set the maximum number of failed logon attempts to 3:
UPDATE DBC.SysSecDefaults SET MaxLogonAttempts = 3 ;
The system does not accept a null value. A zero value prevents locking, and a negative value causes the system to write an error message to the event log at the next restart.
You must have the DROP USER privilege to execute the MODIFY USER statement.
For a discussion of the GRANT statement, see Working with User Privileges in the Database.