RM1528 | Amending an existing annual claims case: Introduction
From HM Revenue & Customs · Repayment Claims Manual
When you have set up a case you can use CZ to amend any details.
The rules for making entries in each field are the same as for setting up but you need additional information in the following situations
You can also go from CZ to CL without having to complete Prime Format. Instructions for this are at RM1544.