how to unlock Use the Steam Mobile App for two-factor authentication?

[Therapy]

i tried 3 times to unlock this achievement, but nothing work....

help me!

[Glimmer]

Open up your account settings and change your Steam Guard settings to "Get Steam Guard codes from the Steam app on my phone"
https://store.steampowered.com/twofactor/manage

On a Windows/Mac/Linuc machine, log in to Steam (may require logging out first), this should trigger the New Device check and prompt you to enter a code generated by the mobile app.