updating apple watch series 3

I have series 3 apple watch which keeps rebooting, i have just got new iphone 14 and i am trying to pair with phone. when pairing it says it needs to update watch to 8.7.1 however the watch will not stay on long enough tocomplete this update meaning i cannot set up watch i am completly stuck on how to fix this i have tried resetting phone and watch but nothing works. does anyone know how to fix this or is watch now rendered obsolete by this issue