Hi
khrizmarie11Thank you for your asking. Kindly provide the information below so that we can better assist you.
1. Model Name: Settings>System>About phone
Refer to the link below to check the model name by model no. in the link
https://www.asus.com/support/FAQ/1014441/2. Your current firmware version
Settings>System>About Phone>Software information
3. Can't you download Yahoo Mail app from Google Play Store?
4. If you had download Yahoo Mail app before yet yo can not find it, please try
Settings>Apps & notifications>See all apps>3 dots on the top row>Reset app preferences