To my knowledge, if you used the citation feature when you wrote the cross-reference in note 25, then the cross reference will automatically be updated any time footnote 15 has its number changed.
If you didn’t use the citation feature, though, I don’t think there’s a way to automatically update references like the one found in footnote 25.
well, but I did use it on a previous paper I was writing, without useing the citation feature. it was something about selecting all and a function key, but when I tried to do it again, it didn’t work - inserted codes for all of the footnote numbers.