old topic, but i had a similar problem. This is my solution:
In a RG I have Previous action date (text), and Next action date (input). I want to move the current action date to show up under Previous action date when I create a new Next action date.
I created a third field in the RG that searches for ‘all actions:count-1’
The previous action has :item# and takes the value from the third field that counts the total number of actions minus one.