How to enable Activity reassignment button in CRM Desktop

I have modified below code

if (ctx.form.ActionToEmployee != null)

{

// Employee MVG

register_mvg_dialog(ctx, "Employee", "ActionToEmployee", "btn_mvgEmployee", { "use_autocomplete_list": true });//C9925345

ctx.form.btn_mvgEmployee.enabled = true; //C9925345

}

}

Here I have set autocomplete to true and and also the button enabled is true.Anything else I need to check ?