The article outlines the steps to Backwards Plan a Task on a Job
FOLLOW STEPS BELOW:
1. Open the "Product Costings Window"
2. Open your desired Job (Use filters If needed)
3. Right Click the Task you want to Backwards Plan against (It has to be Delivery Step)
4. Select "Backwards Plan"
5. Enter the date for the Target
NB. For a quick tutorial watch below: