App won’t open. Yahoo Mail

In common with many other Mail providers, Yahoo now use App Passwords to secure access IMAP or POP3 mailboxes.

The Mail App on each of your devices, such as your iPad, requires a unique password to be generated from within the Yahoo account. This App password intentionally differs from your Yahoo account password - and can only be used to access your Yahoo mail.

More information can be found here:

https://help.yahoo.com/kb/SLN27791.html

What u can look on ipad if u have remote profiles or vpn at seetings/general if not try to reinstall it Or Call the devoloper apple cant help u with third party apps how they work