By design, It is not possible to add a direct transition from another workflow action back to the first action. For example, if after the second action you need more information from the requester, you have to create another action for the requester, as shown here:
The first action can not have a transition line back to the action. The only inbound transition allowed for the initial action is a self-referencing loop (save as draft).
One work around for this is to include a sync bar with the assignment method of automatic to the system as the initial action and then have your first user interaction be action two and set to the assignment method of automatic to the requester. This increments your action count though, so action two is really your first action of consequence. Once it is the second action though, you can have other inbound transition lines into the action.
Please excuse the old version image, but here is a graphical representation:
With that said, I find it better to have subsequent actions that are configured for sending back to the requester. Your milage may vary, but I think adding the extra actions is both clearer and easier to maintain over time.
Thank you Eric for the workaround, very helpful!