If you are the Network Admin, there will be a "Merge Case" link located beneath the [Alerts] tab. Watch the overview video below:

If you are NOT a Network Admin, you will see a "Flag Case" link (see screenshot here).  There, you can quickly send a message to your Network Admin, then, they can perform the appropriate action on your behalf. Your Flag Case messages could look something like this: 

"[Network Admin], I noticed duplicate Cases in the system. Would you please merge the two cases for John Smith (DOB: 01/01/1950; C1234 and C9876)? Thank you!"

Here is a link to video you may find helpful: https://vimeo.com/97442551#t=420s