Sometimes this may be needed if the IP address changes for the host...for example if using an EC2 image that gets a new static IP. Use these commands (the lsnr and DB must be running first):
1. Drop the OEM DB
./emca -deconfig dbcontrol db -repos drop -SID orcl -PORT 1521 -SYSMAN_PWD
2. Create the new OEM DB
./emca -config dbcontrol db -repos create -SID orcl -PORT 1521 -SYSMAN_PWD
