Hi Amanda
This can at first seem like a really big mistake but it's actually really easy to correct in Reltio. Here's what you need to do:
1) When you are looking at the Profile screen for the record (that's the screen that launches when you click on a record from your search results), you will notice a series of icons down the left side of the screen. The one you want to click into has 3 arrows pointing toward each other (we call this the crosswalk screen). This screen essentially holds the map of how the data was merged together.
2) Click on the crosswalk screen and it will open up a colorful view that shows you the individual contributing source values for each attribute of this record. Each color represents a different source and you can see the source records that are contributing to this consolidated profile listed on the right side. If you hover over a source you will see which attributes that source supplied. The little map on the top right is the key to being able to unmerge an incorrectly merged record. I would now click on the grey box that represents the record I want to unmerge and a little unmerge icon appears.