Just connect your Kindle with your PC via any ISB cable, and with little moving around you can locate the directory where your downloaded books dwell. Just copy it to your PC, and then tranfer to your Kobo reader.
There is a DeDRM plugin for Calibre but it doesn't work very well on Amazon's KFX format. People get around that by getting Amazon to deliver the book in an older format but then you lose the typography improvements that come with KFX.
It feels like this is the beginning of the end for ebook DRM stripping.
The files will be in .mobi and .azw3 format.