Help with republishing process?

Does anyone know of an article or podcast that gives step-by-step instructions for me to self-publish my previously published books? Online searching has been frustrating and fruitless. I have all the files (the publishing company closed). I have purchased a block of ISBNs with my LLC. But do I need to “unpublish” the old ISBNs somehow before I assign the new ones to those same books? Do I need to “unpublish” from kdp and start over, or can I just update the info on my current listings? It’s a multi-step process, and I don't want to do it incorrectly. 😂 Thanks for any help!