Hello i'm new to music theory and im trying to apply basic scale theory to form the chord mentioned above but it im not getting the notes required to form the chord.

This is what i did.
C#m is the relative minor of E major, so the scale starts with the sixth degree of the major scale which gives C#,D#,E,F#,G#,A,B,C# as the natural minor scale.
So C#,E,G# gives the chord for C#m.
But for C#mb6?? C#,E,G#,Ab ??? 
Its for the flat sixth that i don't understand.