How to resolve this Syntax error
Wires need blocking assignments (=), not non-blocking (&lt;=). You can define it this way:

wire In3 = Data[3], In2 = Data[2], In1 = Data[1], In0 = Data[0];


Example here

More commonly you will see the declaration and assignments as separate statements. The two are functionally equivalent

wire In3, In2, In1, In0;
assign {In3, In2, In1, In0} = Data;