erase my data from iPad air

If it cannot power on, then there's no way to erase any data from it.

You can if it still shows up on your devices list in iCloud.com send the erase command to it, so if it ever powers on and connects to Wi-Fi it will immediately erase itself.

Click here ➡️ Erase a device in Find Devices on iCloud.com - Apple Support

An iPad that cannot be successfully restarted cannot be erased.

While the iPad can’t be erased, consider that all locally stored data is encrypted. Unless the iPad can be powered-on - and the Passcode known only to you is successfully entered - no data can be accessed by anyone.

The encryption keys that secure your locally stored data is securely held in the iPad security chip (a.k.a. the secure enclave). Your Passcode unlocks the security chip - which in turn releases the encryption keys necessary to decrypt locally stored data.

No Passcode = No encryption keys = no access to data = secure