First of all, you have to reach adventurer rank 20 to unlock Aloy. Or you can wait until October 12 when Genshin Impact’s 2.2 update comes then you will get her even if you are lower than rank 20.
Once you’ve reached rank 20, you will receive an in-game mail. Open the mail and claim Aloy, you will also get her predator bow. After restarting the game and she will be available on the character select screen.
How To Unlock Aloy In Genshin Impact on Mobile & PC
If you are playing on PC or mobile, you have to wait until November 23 to unlock Aloy in Genshin Impact. She will arrive on these platforms with the 2.3 update. Though you can do a trick to get her right now, if someone close to have a PlayStation, let him/her play on your account and unlock Aloy. This game supports crossplay so Playstation saves carry over to all platforms. That’s how you can play as Aloy on PC and Mobile for now.