Depending on your 'Fire' model and PC, set them up to connect - lots of assistance via Google search. You need to fiddle with 'Settings'/ Device Options). The tablet will then show up as a drive in your PC (suggest you only connect via USB2 port).
Set the tablet up to run Google 'Play'
https://www.howtogeek.com/232726/how...n-fire-tablet/
Load the Aldiko book reader from there
Load any epub books from Calbre into the ebooks folder on the tablet