How does one say: adding a record previously omitted
I might say that I have rectified an omission.
As an example from the Cambridge dictionary, we have
We have rectified this common omission.
"rectify" often goes with "omission".
A very succint way to notify an error, in particular when there are several of them, is to write down an errata section (singular: erratum) or an ADDENDA (singular: addendum) at the end or at the beginning of the document.
ERRATA (from preceding edition)
XXX p. yyy is now WWW
UUU p. VVV is now PPP