How do I transfer my iPad protection plan to the new device?

Presumably you refer to an AppleCare+ plan. These cannot be transferred to a replacement device - however, you can cancel an existing plan and potentially receive a refund for the unexpired portion of the plan:

Cancel or change the payment method for your AppleCare plan - Apple Support

If you require the benefits of an AppleCare+ plan for a replacement iPad, you will need to purchase a new plan.

Protection?

To what type (or types) of protection do you refer? Do you have a particular problem or issue that you need to resolve?

With more information and a better understanding of what you are attempting to achieve - or the issue that you a trying to address - contributors here will be better able to provide appropriate help or guidance.