I have some of the dnd books in real life and was wondering if I had to rebuy them for dnd beyond or if I could somehow get them on the app instead of repurchasing

It's a frequent question.  The answer has always been no, owning a 5e D&D book in hard copy does not grant you any free access to D&D Beyond's digital versions.  If you want to read on the logic, and potential future models for D&D Beyond's relationship with physical books, you may want to check this FAQ in the forum you posted:

https://www.dndbeyond.com/forums/d-d-beyond-general/d-d-beyond-feedback/96069-hardcover-books-d-d-beyond-and-you-faq

Yes, you have to rebuy them. In the future you should be able to buy bundles that include physical + digital.

Here is your official response:

Quote from Stormknight >>

Unfortunately, there is no possibility of backwards granting access to content on D&D Beyond, for free, based on physical books you already own.

On top of other reasons, there is no way to legitimately discern who has purchased a physical book (barcodes/receipts etc are not viable).

With regards future book purchases, we are exploring options. We're not able to share what that might look like as, at this point, it's still exploratory.

Whilst probably not the answer that you wanted to read, I hope this provides the answer requested.

And to update: https://www.dndbeyond.com/posts/1310-faq-one-d-d-rules-d-d-digital-and-physical-digital

Digital & Physical Product Bundles

What are digital and physical product bundles?

We’re excited to offer our first ever selection of specially priced bundles that give you a physical copy and a D&D Beyond digital copy of the upcoming book Dragonlance: Shadow of the Dragon Queen. Our first offering is now live on dndstore.wizards.com.

Can I expect more D&D products to offer physical and digital bundles?

Yes! We want to deliver on this ask. Right now, we are in the test and learn phase. Join us on this first foray and expect more in the future. For now, we’re not quite ready to commit to every book getting a bundle.

You called this bundle a test. What are you testing?

We are testing everything from distribution method and quantities to bundle contents. We thought it was important to call this out as a test because you should expect things to change over the next two years while we work on bringing more D&D in more ways to more people.

Does the bundle come with preorder perks?

Yes, all preorder perks you would receive on D&D Beyond are included in this bundle. A preorder perk exclusive to this bundle is early access to Shadow of the Dragon Queen on D&D Beyond. Players who preorder the bundle will be able to access the D&D Beyond digital book starting November 22, 2022.

How do I redeem my product on D&D Beyond?

When you purchase a bundle, you will be asked to provide an email address at checkout. You will later receive instructions via that email to access a code that grants you early access to the product on D&D Beyond. Your code can be redeemed at: dndbeyond.com/marketplace/redeem-key.

If I have purchased a bundle on D&D Beyond that discounts products, will that discount apply to this bundle?

No, those discounts only apply to products purchased directly on the D&D Beyond website.

Is there a way to get this bundle and support my local game store?

We love our friendly local game stores and we know you do, too, but at present this test bundle is limited to online purchases directly from dndstore.wizards.com. It is not available through any other store or marketplace.

I already preordered my book physically or digitally on D&D Beyond. Can I swap it for the bundle?

We do not have any upgrade paths to the bundle at this time. You would need to work with that outlet to request a refund.