Hello, I’m Nathan, and I’ll be assisting you today. My livelihood depends on your positive feedback, so your satisfaction is my highest priority.
Sorry to hear you’re having trouble.
You actually don't have to do anything special.
So long as you register the new kindle to the same amazon account as the old one, all of your prior content is automatically available on the new kindle.
Go to the HOME screen on the new kindle (after you have completed the initial setup steps of wifi setup and registration) and then look for the CLOUD library.
There you'll see all your previous purchases, upon selecting any of them, they'll download on to the new kindles "local" storage and be accessible to you there anytime.
Let me know if you get stuck along the way,