Hi
When updating a cards due date I want to update the linked card's due date to the same date + 3 days.
I guess Butler is right for the job.
I've got this far.

I think the steps are.
Trigger: on set due date
Action:
Step1: find linked card
Step2: set the same due date on the linked card as first card (can't accomplish this one)
Step3: add 3 days to due date