When you're logged in to your Kobo Writing Life account, click on the book you'd like to add to Kobo Plus. You can select to include your book in the Rights and Distribution section of your title.
When you're adding your book for the first time, you'll be prompted to accept our Addendum to our Terms of Service. (Here's a link to this, for your reference.) You'll only need to accept this Addendum once.
Please note that while there's no exclusivity required with Kobo Plus, you are required to keep your books in this service for no less than 90 days.
Once you've selected to opt in your title, all you'll need to do is click Save and continue and your title will be made available once it's published. If it's already published, all you need to do is save your changes.
If you'd like to bulk opt in your books, please let us know by submitting a request above. We can manually opt in these titles for you.