How to pass subclass to variable of super class ?

class /EVUIT/EXCH_PRD_GUI definition

public section.

  methods CONSTRUCTOR
    importing
      value(I_APPLICATION) type ref to /UIT/EXCH_PRD_APP optional
      value(I_REPID) like SY-REPID .

class /UIT/EXCH_PRD_VERT_NN_MODEL definition
  public
  inheriting from /EVUIT/EXCH_PRD_APP
  create public .


DATA: l_vert_nn_model type ref to /uit/exch_prd_vert_nn_model.
DATA: l_gui type ref to /uit/exch_prd_gui_vbeleg.

   CREATE OBJECT l_vert_nn_model
        EXPORTING
          I_ALV_RECORDS = gt_alv_records[].

CREATE OBJECT l_gui
   EXPORTING
     I_APPLICATION = l_vert_nn_model
     I_REPID = sy-repid .{color}

Problem i am facing is for l_gui the parameter i_application is of type super class of l_vert_nn_model.

Any suggestions, how can i pass this subclass object to the parameter which is of type super class?