During the working life of a 3000A Series Calibrator, it is quite normal for adjustments to be performed to remain within nominal specifications.
This process can be performed by any laboratory with suitable equipment.
Transmille has published a full calibration guide for the 3000A Series Multiproduct Calibrator which can be downloaded from the bottom of this support article.
For experienced technicians who do not require the full manual, there is also a quick start guide available, once again attached to this support article.