How to seperate three phase signal to three single phase signals in matlab?

i have an system with a 3 phase measurement block from which i get a 3 phase voltage measurement (Vabc). Now i want to use OLTC to control that voltage but since it is an unbalanced system i need measurements of all 3 phases separately and then independently control the voltages of all 3 phases (Va, Vb, Vc). But how can I get those 3 separate signals? The demux block gives dimension error.