modify primary key

How do I add a existing column to a composite key in an index organized table on Oracle 9i?

create table mytable (
mycol1 number,
mycol2 number.
mycol3 number
constraint myconstraint primary key(mycol1, mycol2) ) organization index;

now i need to add mycol3 to the primary key. Received on Tue Oct 31 2006 - 11:45:30 CST