At this time, only the adult account holder is able to update the address on the account.
From the parent's Copper app,
1️⃣ Tap on the 'More' ⚙️ in the bottom right corner.
2️⃣ Tap the very first icon at the top with your name under it.
3️⃣ Tap the pencil edit icon next to your current address.
✅ Update your address from there. 👍