I call the contact center and they advised to write a LOE
That illustrates
the difference between an application still pending and one that has been finalized.
For sure, if someone realizes they have given inaccurate information, or omitted information that should have been disclosed, in an application which is still pending, that's a no-brainer: communicate a correction with explanation.
Once the process is finalized, there is no way to correct information in the application.
A correction with explanation (LoE) may not fully resolve things for an application that is still in process, depending in part at which stage of processing it is, depending more on the nature and scope of inaccurate or omitted information, but should go a long way toward avoiding an allegation of misrepresentation, and will generally mitigate the negativity of the error otherwise.
Should be obvious, but of course if IRCC has already identified and is questioning about the matter, it is particularly important to make a correction and give an explanation, but that's not nearly as helpful as making the correction sooner.
After the fact . . . the situations I was addressing . . . what's done is done. There is nothing pending for which a LoE would be relevant.
In any later application, if the same information is involved, then the correct or complete information should be given (focus on being accurate, honest, and complete, even if there was inaccurate or omitted information in previous applications), and depending on how much of a discrepancy that is compared to what was submitted in the previous application, maybe include a LoE (explaining there is a correction as to information given in a previous application, identifying that application in particular, and explaining why it needs correcting).