When you're logged into the MLS navigate to your main dashboard. Look for the PropDisc tile. When you click on the tile PropDisc will open. If you already have an account you'll be signed in and dropped onto your PropDisc dashboard.
If you haven't yet created a PropDisc account you'll be prompted to create your account on PropDisc with a one-time passcode. You'll only need to do this once and then the SSO will automatically work each time.