Modify a value in Firebase in Swift for IOS

Have a question in Swift for Firebase.

Here's what our JSON tree looks like. We would like to rename the second Billy, to lets say... Frank

I suppose we start by selecting the Parent Key of LSXz631YH9gTJlVwJKs? Then modifying it's child Name to "Frank"?

How do we select the second child "Billy", and then change it to "Frank"? (notice the first name is also "Billy") :(

Is there a way to do that?

Any help is greatly appreciated. Thank You!