If the Kobo plugins (there are more than1) have been installed, your conversion options should list
KEPUB (only needed if you was a Kobo copy on your PC) as an outbput format.
With the device connected, Configure Device: tick KEPUB
Make other changes (on tabs) to taste The last tab has send as kepub

Kobo's can also work with EPUB (and ADOBE DRM if you register the device like any other Adobe) without any effort /conversion