Turn on the bike. Go to add sensors on the Garmin and find the Ep8 display and connect. The Garmin will then set up an extra sTEPS screen automatically, but you can also make your own custom ones.
It's not much different to adding something like a heart rate monitor.
Gordon
p.s. you're connecting via the display. So if your bike has the cheap 5003 controller it won't connect. You need the SC-E800 or SC-e7000 or EN-EW 100 junction box.
I dont think this works with all / many Garmin devices. I cant get my Garmin 520 + to connect to my EP8 Bullit. It used to connect to my Gen 2 Levo just fine.
I'm sure ive seen a list of only 3 or 4 Garmin devices that work with STEPS to give the key metrics of Mode; battery % & cadence.
If anyone has got these working with a Garmin 520 plus, please let me know how.