Hi.
About the Site Minder admin:
You need to ensure your SM administrator has full administrative rights. Then you shall use Site Minder itself to change his password, then log back into SM from their WAM UI and confirm the new password is working. Then, to effect that in Identity Manager you shall: Stop all your app servers that use this siteminder administrator in their ra.xml, use the Password Tool to encrypt the new password of that administrator and paste it back to the ra.xml in all app servers, then start them back up and confirm the connection is made in IDM startup step 2.
About the IDM store admin:
I guess you refer to the LDAP administrator account of the corp user store as specified in the directory xml. If this is what you are asking for then you shall use an LDAP Browser to change that password and log into that directory server with the new password to confirm it's correct. Then, you shall export the dir xml and encrypt the new password (using IDM password tool) and update that dir xml back using the /iam/immanage.
About the etaadmin:
I don't know, hopefully someone else will answer that.
Thanks,
Sagi