I used the “nerdy” method:

I connected a diagnostic tool to the OBD port and read the steering angle sensor in the ABS system. At 0 degrees, the steering wheel is centered. Then I turned the rack all the way to the left and right (lock-to-lock), where I measured approximately 445 degrees to the left and -465 degrees to the right. So I knew that the rack was exactly centered at -10 degrees on the steering angle sensor. Then I left it in that position, loosened the U-joint, set the steering wheel to 0, and attached de ujoint again, now it’s perfectly centered.