Hello Supanat.c!
Welcome to the Microsoft Office Community Forum. Thank you for sharing your concern with us today and we hope that all is well.
I understand your concern that you wanted to know how you can turn off the Microsoft Authenticator App. Let's us check on this together and sort this out. Rest assured, I will do anything that I can to assist you with your concern.
To further assist you in turning off the Microsoft Authenticator is that, you cannot just delete right away the Microsoft Authenticator app, because if you do this you might loss access in to your account. You will need to turn off first your two-step verification on your Microsoft Account or any account that you've associated with your Microsoft Authenticator app. After that you've cleared or turned off your two-step verification on your account, then that's the time that you can remove the Microsoft Authenticator app on your device if you don't want to continue using it.
To turn off your two-step authentication on your Microsoft account, you may consider the instructions stated on this article. How to use two-step verification with your Microsoft account

Hope it helps. Please let us know if the you have concern about this.
Sincerely
ReynaldoB
M365 Consumer Forum Moderator
Microsoft Community