I'm trying to just export all blocks which belonged to a folder and then import to another environment, however from the exporting page, it's just showing page, not folder or block. I don't know how can I do that with EPi admin functions
The short answer is: You can't do it in default Epi admin.
A workaround would be to copy the block folder into a page folder (For this page) and then export the page. All page assets are exported as well. After import you can just move the folder if you want to.