I may be wrong, but I don't believe crash reports are accessible in android. It might be a developer feature, I'm not sure.
I think the easiest way would be to debug your client's phone and check the errors through the compiler.
Or use try/catch, and log to a file whenever an exception is thrown.
ex.
File.WriteString(File.DirRootExternal, "log.txt", "SendFileToDatebase args: " & param1 & "," & param2 & " " & DateTime.Date(DateTime.now))
Put a try/catch around each of your functions, and write that function name + parameters to a log file. That way you know where the error occurs, and what parameters might cause it. You can write the original error message too.
You could even send your function exceptions to a webserver.