Hello @AndyD41 ,
For automation series, if you're needing to add more steps to the series, for the time being you'll need to create a new series and give it respectively adjusted timing / open triggers based on the previous series. Or, you can cancel the current series, copy it, and add the additional steps to the Draft copy, before activating.
I've tracked your feedback for our engineers. If and when they have an update to this feature request, they'll make sure to notify you.