Unfortunately, without the additional information requested in my first/previous response, I will not be able to give you detailed advice to your question, but I will be able to give you a general answer, which I hope will be of assistance. If you are able to supply the additional information later, please do so and I will then come back to you with a more detailed answer.
There is no standard form or rule to be followed to use facial recognition.
Different forces will have different rules, some may not even use the system.
It is primarily used to trace and track suspects involved in serious crime. It is not used commonly for missing persons. It may be for a missing child, but adults less likely, they may be missing or they ay simply do not want to be found.
As for the sharing of information, that falls under data protection laws which themselves are a minefield.
You have no automatic right to know what is on file for a person. A court order can demand release of information if there is an ongoing case.