what output style are you using? – You can NEVER EVER edit an endnote generated field (the grey text when you hover over it). It will always revert the next time endnote updates the fields.
You need to enter the cited paged thru the edit citation function AND you need to ensure that the output style for footnotes (or citation template if the footnotes follow that template) have the cited paged field included and that the appropriate characters to ensure associated punctuation is not included when no cited pages are entered.
So back to - “What output style are you using?”
You need to learn how to edit a citation, right click in the footnote and select edit citation>more and enter the cited pages in the appropriate field). If it doesn’t work, then you need to (or ask here, for someone to help) edit the output style to include that field.