Is your feature request related to a problem? Please describe.
Let's say I open a page, if I want to change page I must exit the GUI and reopen it to then go to the page I want.

Describe the solution you'd like

It could be done by like adding the option to open ender chest specific pages using commands, and then setting the arrows to execute that command.
(I never made plugins so I don't know if it's even possible, but I programmed a little bit so I think that it could be done by creating a variable like "currentPage", shown as name of the paper like "Page " + currentPage, and then for the arrows execute /echest page (currentPage + or - 1). As I just said I don't know if it's even doable, it's just an idea)