Can You Edit a Cover or your Interior on Amazon KDP?
Yes you can do this easily. Keep in mind a couple of things, Amazon will review your book again and changes should not be a radical change from what you previously had.
Once you have edited your Cover or your interior and have your PDF(s) login to your Amazon KDP account.
Go to your bookshelf and find the book you want to update and click on the ellipsis (...) button and choose "Edit Print Book Content".
Scroll down until you get to the manuscript part and click "Upload paperback manuscript", click on it and uplaod your interior PDF.
Then click "Upload your cover file" and upload your cover PDF.
Wait until both are done uploading and say, uploaded successfully.
Be sure to click on the "Launch Previewer" and preview your book.
Click on save and continue on bottom right, then it will take you to step 3 and do the same on that page.
You will have to wait for Amazon KDP to approve the changes, in the meantime your older version of your book will continue being listed and sold on Amazon.
Once approved your new version will be sold.
If you have A+ Content on your book you just edited, don't forget to update it as well to reflect any changes you made.