There is no calibration.
This just happened to me after my annual, where I pulled two of the probes, and suddenly one of them was 200F low. In the end, the issue was that the probe got bent and abused when it was removed, and that caused it to read low.
Likely, you'll need to replace the probe(s) that are low. Very few failures will cause them to read a little high.
At the same time, if they messed with your fuel system, you may actually have a spread like that. One thing to do is a lean check and see if they all peak at the same time or not. If they peak at the same time (approximately) then your EGT is likely wrong. If they peak all over the place, then you have a fuel distribution issue.
You can also swap the EGT probe from your hottest cylinder to the coolest and see if it follows the probe or the cylinder.