Means, the accounts he wants to have deleted need to be downloaded into outlook (emails), exported into pst and then imported into info@cobaltbkk (also check/export the onedrive). Then you can delete those accounts (no need to put them into shared, since we have the emails into info@cobalt).
This would free up some licenses used for sysd and others requested users . Hope I was able to explain this in a better way, feeling a bit groggy.