There's a couple of ways to add databases. Either should work if your host and agent are already discovered (and up/green) in EM.
Setup -> add targets -> Auto discovery results
Click on the tab that says Targets on Hosts (might be different in 188.8.131.52 -- 2nd tab).
Here you should be able to find the database target that you're trying to discover, click on it and click Promote.
If it's not there, you can try to discover targets on that host by going to Setup -> add Targets -> Configure Auto Discovery, find the host, and click Discover Now/Run Discovery.
If these fail, try Setup -> add targets -> manual -> guided discovery (2nd bullet)
select option for oracle database, guided discovery
Then instead of typing in the hostname, click the search icon (magnifying glass) and search for the host that way.
Hope this helps.
ok, I will try those steps first.
I still got same issue.
If I search target name, it shows up the hostname info, if I click it, it will show the host information, blah blah.
However when I try to add database target, it will say add host first, it cannot find that hostname.
Did I miss anything here?