Last Year, storms in the UK caused damage to my Netatmo outdoor module, it became permanently disconnected from the indoor base station.
The iPhone app seems to require a working module to remove it, i.e. it wants to connect first before letting you delete it, which not only is a bit weird but of course doesn't work if the module is broken. After logging a ticket with Netatmo's support team, they eventually shared these two links...
With this, you can connect the base station to your Mac/PC and delete the modules from there, nice!