Shift operator (q) used in system identification, if we choose a polynomial models like ARX, ARMAX, BJ, and OE. Since version R2009b q is defined equal to z. In these models have always used the backward shift operator (q ^ -1), not a forward shift operator (q). To apply q ^ -1 we only define the model parameters: B (q), F (q), C (q) and D (q), which is the coefficient of the model by: (1) choose one of the models in system Identification Toolbox of Simulink (2) double-click the selected model and then write the coefficients in the "Orders of the model [nb nc nd nf nk]". Hopefully, in accordance with the intended.

OK.

But what should be done if for identification I am not using ready system Identification  toolbox in simulink but my own code using RLS algorithm using s Function.

How to implement backward shift discrete-time operator [delta] in MATLAB simulink?