First, log in and verify the account matches what you ordered, characters, currency, and server, before making any changes.
Once you've confirmed everything is correct, follow your game's login and setup guide for the exact steps to secure it. Timing and steps vary by game: HoYoverse accounts (Genshin Impact, Honkai: Star Rail, Zenless Zone Zero) need several days of active play before changing any account details, other games can typically be secured sooner.
Find your game's guide on the Help Center home. For games where the email cannot be changed, full access to the original email will be provided so you can manage it yourself.