Here is the video of how to make the cover and how you put the booklets into the cover to assemble the planner. For the cover, you can use felt, fake leather, real leather, cork… If you want to use cork, you need to use a cork fabric, as normal cork for pin boards will break. I recommend the cork fabric from Cork Lane: https://shop.portugaliacork.com/
If you need some inspiration check out my Pinterest board for this method: https://www.pinterest.at/corlissblackbeard/bookbinding/replaceable-book-blocks/