In order to play chapter 5, you will have to download it, unzip it, and copy it into your chapter 1-4 folder. If you get a question if you want to overwrite some files, you are doing it right. Click Yes to overwrite.
The reason I had to do this was because of the Itch.io file size limit.
Alternatively, you can go to my Patreon and download chapter 1-5 in one go (link above). Your saves will still work even if you unzip it to a different folder.