Stone-Seeder Hierophant does not have summoning sickness.
You have a creature card in hand that can be cast using three in any combination of ({W} magic symbol) and/or ({U} magic symbol) , and have the mana to cast it.
Steps
Cast the creature in your hand by paying its mana cost.
Chulane triggers, causing you to draw a card and put
Azorius Chancery from your hand onto the battlefield.
When
Azorius Chancery enters, it,
Stone-Seeder Hierophant and
Retreat to Coralhelm trigger.
Resolve the
Stone-Seeder Hierophant trigger, untapping it.
Holding priority, activate
Stone-Seeder Hierophant by tapping it, untapping
Azorius Chancery.
Activate
Azorius Chancery by tapping it, adding ({W} magic symbol) ({W} magic symbol) ({W} magic symbol) ({U} magic symbol) ({U} magic symbol) ({U} magic symbol) due to
Nyxbloom Ancient.
Resolve the
Azorius Chancery trigger, returning it from your hand to the battlefield.
Resolve the
Retreat to Coralhelm trigger, untapping
Chulane.
Resolve the creature spell cast in step 1.
Activate
Chulane by paying ({3} magic symbol) and tapping it, returning the creature from the battlefield to your hand.