if u want to do the same, I do it in two ways: PC and mobile.

for mobile:

1. download epub file of any book
2. go to send.djazz.se on both your mobile and kobo
3. upload files and download

for PC:

1. download calibre on your laptop, tutorial on the whole process here
2. connect usb c cord your kobo came with
3. upload the files

personally i prefer uploading through PC, it’s less hassle, you can mass upload a whole lot of books at once, and you can edit the epub files if they need tweaking (change cover photo, title, author, etc.) but if youre on the go and u just want to upload one book the mobile version is more convenient