You're screwed! You will have to set it back up from scratch. Do you have a recent backup you can restore from?
Be warned, a network reset on the phone will result in the end user having to reset and setup their watch from scratch too!
My advice comes from being a UK
Samsung iPhone user.
Current Devices:- iPhone 14 Pro 256GB Deep Purple
- Samsung Galaxy Buds+ > Model: SM-R175.