How to override a step of cataloged procedure from JCL?

How to override a step of cataloged procedure from JCL?

//MYJOB   JOB  (,,)
.
.
//MYPROC   EXEC  PROC_NAME
.
.
//STEP_NAME.DDNAME

STEP_NAME = Name of a step from given cataloged proc PROC_NAME
DDNAME= DDNAME of given step STEP_NAME.