First you need to configure an LLS device connected via RS485 port in a configurator.
Set RS485 mode to LLS, set baudrate according to your device's specification and select your device's ID from LLS X Address drop down list. If your sensor is connected properly ID should be displayed.
Then depending on which LLS address you have assigned your ID, data of your sensor should be visible via configurator. If you want it to be sent to a server set it to Low priority. Then your sensor data will be attached to every periodic record that FM device sends.
Make sure that your sensor's protocol is compatible with a FM device you are using.