How do I disable Hide My Email on iPad Air?

Hide My Email is a service which comes with an iCloud+ subscription. You can use it or choose not to. It isn't turned on or off.

Apple's support page How to use Hide My Email with iCloud+ on your iPhone or iPad - Apple Support shows you how to deactivate or delete an email address used in Hide My Email. If you take these actions the email addresses in Hide My Email which are forwarding email to your primary iCloud address will cease to function.

if you mean how can you stop being offered Hide my Email in Safari every time you try to enter an email address, no you can't stop that at all.