new ipad cannot open

• Settings>Mail>Accounts... tap on the incorrect account... then on "delete account".
• Restart your iPad
• Use these instructions to add the correct email account:--> Add an email account to your iPhone, iPad, or iPod touch - Apple Support

Regards

Giulio

If you're sure you added email account correctly in Apple Mail app, check:

Settings>Screen Time>Content & Privacy Restrictions>Allowed Apps>.... Mail must be ON (green). When done, restart your device.

If you mean something different, please specify your needs/problems better.

Regards

Giulio

My pleasure