Is there a way to downgrade an Apple Watch SE 2nd gen to watchOS 9?

Hello, my son’s watch was recently replaced under warranty to a SE 2nd gen(40mm + cellular),but his iPhone 7 doesn’t support the iOS v17 required. If we pair it with one of our iPhones then it will be associated with our Apple ID/device and he can’t call us. Can anybody suggest a solution where it can be associated with his Apple ID without us buying a new iPhone to pair it to? Thanks in advance.

[Re-Titled by Moderator]