If you want to turn your physical book into a Kindle book you can just ask your formatter to also create a Kindle version of your book for you. They can usually do this in a short amount of time with publishing software. Having a Kindle version is a good idea because so many people love to read from a device.

If your formatter does not format for Kindle then try there are many people who specialize in creating this kind of format.

You can upload on KDP just like you uploaded your physical book, they will walk you through it on the KDP site.