Software update on Apple Watch SE Gen 2 taking forever

Bought a new Apple Watch SE Gen 2 and trying to pair it with my Iphone 13 pro max. Stuck with software update. It will go from 2 hrs remaining time down to 1 minute and will go up to hours again. I tried everything. Reset both iphone and watch, both device is fully charged and connected to the charger, im using 5G wifi also. What do i have to do???