With value specification actions you can introduce values which you can then use with object flows. You can add them to your diagram by clicking on Action in the toolbox, and clicking on the activity diagram afterwards while holding the CTRL key. There you can select Value Specification which will add a value specification to your diagram.
Note that the "result" pin isn't shown by default. To get the result pin, right-click on the value specification and select "Structural Elements..." where you can select the result pin to be shown:
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