Support FE-C protocol
With the following models, it is possible that the Garmin device controls the brake. The program used by the Garmin device will change the resistance. In most cases you can set your Wattage target power and the brake will adapt. With the Garmin 1000 it is also possible to ride GPS tracks were the program will control the resistance (like with Tacx Trainer Software or Zwift). Connect the trainer as indoor trainer.
Make sure that you are running the latest Garmin firmware. Check Garmin for updates
All other models can receive information, not control the trainer. The standards are speed/cadence and power profiles. So there is no change or resistance. It is possible to use Tacx software or 3rd party to control the trainer and in an addition disply the profiles also on your Garmin device. The speed shown on your Garmin device is the real speed (when in controlling the brake via another program can be related on Virtual speed). More info on the training section.