Setting up Apple Watch 10: no room for 6 digit passcode?

I'm setting up a new Apple Watch series 10 for my son. In order to access my son's "end-to-end encrypted data stored on iCloud," I was prompted to enter the passcode on his iPad.

However, his iPad passcode is 6 digits. But the Watch only provides space for 4 digits.

I tried a few 4-digit variations and am now temporarily locked out.

Do you know how to enter the 6-digit passcode of another device?