How is the book getting on to the device?The series tab relies on the series information being the same for all the books in the series.
If the book comes from Kobo, then Kobo needs to fix the metadata on their side to do this correctly. Report it to them and they should be able to do it.
If you are sideloading using calibre, then you need to make sure the series name is the same for all books in the series. When that is done, the next time you connect, the driver should fix the series information. That is assuming the options are set correctly in the preferences and driver.
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