Sorry, but I can not help you with that. As far as I know, it is not possible to delete messages using the foodsoft web application.
You are probably disappointed because your message was being ignored for such a long time. If you wish to trigger more replies then consider to open a feature request here: https://github.com/foodcoops/foodsoft/issues
. If you are lucky then someone else replies there.
In general, if there are information in your foodsoft instance that need to be urgently deleted then contact the system administrator of your foodsoft-hosting instance. It is possible to temporarily disable your foodsoft instance in order to analyze the situation and selectively remove the sensitive information. Please be aware that this implies significant effort for the administrators of your hosting instance. In case of the global hosting platform you can send an email to the address shown at https://foodcoops.github.io/global-foodsoft-platform/#support