does astral heron get discount for 2 cards after moving to another battlefield

No — Heron's discount covers exactly one card, and moving him to another battlefield neither grants a second discount nor cancels the first.

The trigger is "when you play your first card each turn," so it can only fire once per turn; relocating Heron afterward doesn't create a new trigger. If the trigger already fired while he was at a battlefield, that discount is locked in and still applies to your next card no matter where he goes (FAQ #11869). Also note the errata'd text says "the next card you play this turn," so the discount expires if you end the turn without using it.