I disabled my Iphone by mistake, how to undo it?

Is it your iPhone or your Apple ID that is disabled?

If your Apple ID, be aware that this is primarily a user-to-user support forum; other Apple users like you. You will need to contact Apple Support. See instructions in: If a message says 'Your account has been disabled in the App Store and iTunes' - Apple Support

or if your Apple ID is locked, Ssee instructions in: If your Apple ID is locked or disabled - Apple Support

If your iPhone is disabled, see: If you forgot your iPhone passcode - Apple Support

If you forgot the passcode on your iPhone, or your iPhone is disabled or unavailable -

How to reset your passcode without a computer if you have iOS 15.2 or higher.

How to remove your iPhone, iPad, or iPod touch passcode without a computer - Apple Support

How to reset your passcode using a computer.

If you forgot your iPhone passcode - Apple Support