Apple Watch keeps asking in pairing with old Apple ID instead of new

A customer has a new Apple watch series 7 that he is trying to paire to his iPhone, but the watch app keeps giving him an old ID, and he lost his password a long time ago. The customer now has a new account ID, but it does not appear on the watch app, knowing that the new account is the one used on the phone I want to point out that I deleted the watch app from the device and re-downloaded it, but without any benefit.