apple watch series 3 got disconnected and it is not connecting to my iphone

my i watch got disconnected from my iphone suddenly and now when i want to pair with my iphone, its not getting pair and asking me for an update and when i try to update it is not getting updated, infact it disconnects the pairing part from iphone, so i removed the device from iphone thought of that it will get connect but it’s not getting paired and not getting update.