EPO prediction is an orbit file to quickly locate GPS satellites and reduce the time it takes to calculate your position.

EPO data is updated each time your connect your GPS to your wifi or Bluetooth to a phone and wifi the EPO data is automatically uploaded in the background and from Garmin I believe stays valid for around 14 days.

On a  Garmin this can be done using the Garmin Connect™ Mobile app on the connected smartphone via Bluetooth on a device that connects to a smartphone.