transfering from Calibre to Nextbook3

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Hello all. New to the forum so appreciate any assistance. I just purchased a Nextbook3 which due to my severe vision problems allows me a larger font and back light which my Kobo does not have. Nice to be to read without a large magnifying glass. To transfer books from Calbre to my Kobo I simply connected the device and Calibre recognized it and placed a device icon on the task bar. It was a simply matter to transfer books one at a time or as many as I wanted to Kobo by simply selecting the transfer to device option. With my Nextbook3 I do not get this feature however I am able to transfer a book by dragging the book to the Nextbook folder in the small window that pops up when you connect. Not sure if I can transfer multiple books this way or if they have to be done one at a time. Anyway I have transfered two books at this point and note that they show up on my Nextbook simply with a blue cover with 'EPUB" on the cover. Although the name of the book is on that cover , it would be nice to have the actual cover . I would appreciate any information on how to correct this or what I may be doing wrong. Thank you very much.

Rick