The box should be secured by a cable tie through the cover, you can see the hole on the right of the cover in the picture, with the main wall fixed part. It looks as if this was not done at installation, it’s possible that the cover was always loose and has just fallen off.
Tudor There are 10 types of people: those who understand binary and those who don't and F people out of 10 who do not understand hexadecimal c1a2a285948293859940d9a49385a2
Welcome to our Community and thanks so much for your first post - so sorry to understand that the cover to your Omnibox has become loose and fallen off.
This has happened to mine in the past and was easy enough to reattach with a cable tie - however, if you're having issues or have any concerns about the cabling, please do let us know and we can arrange a technician to pop by and reattach for you.
Let me know if you've managed to get this sorted yourself or if you'd like me to arrange a visit.