Normally there is no specific setup needed here; everything should just work out of the box.
Maybe the I2C is not plugged into the correct header on the core?
You can see the installation here:
It’s also possible that the cable is bad. Maybe the ports were never noticed as non-functional?
Are the chips installed? Do they have the correct firmware on them?
I think there is a duty of care required from the person who built your unit, so I would suggest to ask them. But we will also help out as much as we can too.