Youtube has a bunch of videos on the subject. Here is the first one on the top of the page to save you time. Not sure of the quality so look at a few videos

https://www.youtube.com/watch?v=7L2Bbevuqs4

Change the author's name and edit pictures with your name/company on it.

Usually, they will come in pdf and doc format. If is pdf, you can easily find online software to convert pdf to doc easily.

With PLR, if you have the source, you can simply insert your own links before converting to pdf. But a good many vendors provide rebranding facilities for the ebooks they provide to promote their products and services.

You can just head over to canva and type out your own version of the PDF. It's a bit harder work, of course... but i think it can't get more "rebranded" then that

You can use a tool called Pixel Studio, but it's a paid service at a one-time fee.

Or you can hire someone on Fiverr to design 3D and flat covers for you.

Remember to change the name of the product and add links to your brand or other related offers in the ebook.

Another option is to learn the basics of Photoshop and rebrand the graphics yourself. But Photoshop can be a real pain to learn, I still hate using it lol