If you wonder what is the password for Oracle Internet Directory(OID) user cn=orcladmin after OIM installation, well, it is exactly the same as ias_admin password specified during installation of OIM. If you really want to reset the password, use included utility resetiASpasswd.sh in $ORACLE_HOME\bin as follows:
First make sure your environment is setup properly for OIM home. (ORACLE_HOME param.)
$ORACLE_HOME/bin/resetiASpasswd.sh cn=orcladmin your_new_pass $ORACLE_HOME
To reset OID password use oidpasswd utility as Robbert pointed out.