Insert "Return value" in the Generic Template (Decision Table) for the "Action Cell Groups" in Dynamic Binding.

By default, when you first create a decision table template, it creates an Action Cell Group with a Display Name of Result and a binding of return, as long as your table has a return type.  I am assuming then that your return type was set to void.  You can still add an additional Action Cell Group, choose a Static Action Cell Group, add a Cell Format to it, and create a template in the table that displays whatever you choose, and in the SRL Content area just says return.  If you create it as an Optional Action Cell Group, you can just add this column in tables where you want it to return and not use it on other tables.