Old Icloud Account with Yahoo Mail

Hello, first of all, please allow me to introduce myself. I am from Vietnam, and my English may not be very good because I will be using Google Translate. If there are any parts of my message that are hard to understand, I kindly ask for your understanding.

A long time ago, I was given an old iPhone 5s from my uncle, and it already had an iCloud account that was created with a Yahoo email address ending with @yahoo.com.vn. After using the phone for about 7 months, my parents took it away from me because I played games too much.

Now, in 2025, I just found the phone hidden under my bed, a place I never thought my parents would put my beloved iPhone 5s. Currently, my uncle’s iCloud account is locked, and I cannot purchase anything from the App Store without verifying the account. However, as you may know, Yahoo no longer supports this type of email, and they have disabled my uncle’s Yahoo account because it has not been used for a very long time.

This means that I can no longer verify through the Yahoo email, and I also do not clearly remember the password of the Apple ID on this iPhone. But this iPhone holds many memories for me, and I would like to use it as a secondary phone because it still works very well and the battery lasts a long time.

Is there any way for me to verify the iCloud account and log out of the old iCloud? Please kindly provide me with some guidance.

Thank you very much for reading my message, and I wish you a good day.

[Edited by Moderator]