Apple Watch series 2 pair with my iPhone but doesn’t download the latest update after factory reset

My friend gave me his old Apple Watch series 2 , I’ve deleted everything and made a factory reset, the Apple Watch series 2 pair with my iPhones XS and tells me that their is a new update for the watch , but it doesn’t download or install the update , I’m stuck on putting my passcode and asking me to leave the Apple Watch on the charger but I’ve let it for a very long time and nothing changes , how can I install the new update after a factory reset