For errors found in published ebooks it is generally recommended that corrections be sent to support@j-Novel.club There are various reasons for that but it basically comes down to it will get seen and addressed faster. It is also important to note that corrections found in the final QC before an ebook is published won’t always be applied to prepub parts on the website, so if the book has been published and you find an error while reading the prepub parts on the site it probably was already caught.