There is no such thing as a neder not to eat. As Popa succinctly pointed out, in general, a neder is only an issur on a ????, i.e. had you said for example, “this bread is forbidden to me today,” that would be a neder.
Whether or not the statement has any validity in any case, is the subject of discussion.
The Ran (Nedarim 2b) brings brings a Yerushalmi that has a disagreement about this question; ?’ ???? and ?’ ???? say it’s nothing, while ?’ ???? argues. The Ran says it is mashma that the halacha follows the majority – that it is nothing.
The Ran’s own opinion is also that it is nothing, and he cites Rabbeinu Chananel, the Ri Migash, and the Rashba who accord with this view.
However he mentions that the Ramban disagrees and holds that it is something. The Ran explains that the Ramban means to say that it is valid as a shevua, and the statement used works as a yad.
L’ma’aseh, the Shulchan Aruch (YD 206:5) brings both shitos but concludes that even according to the Ran you need ???? anyway: ????? ???? ??????? ????? ???????? ?????? ?????? ???? ???? ??? ???? ????? ???? ??? ??? ????? ???? ??? ??????.
There is one more possible way out that I can think of according to the Ramban, and that is that on Erev Yom Kippur there is a mitzva to eat, and if what you said indeed counts as a shevua, well, the Mishna (bottom 16a) tells us that a shevua doesn’t work against a mitzva (though you would get malkos for shevuas shav though…). However this is not so simple, because the Ran (8a) is of the opinion that something learned from a drasha is not included in this, and a shevua would work against it. I do not know how we pasken in this shailah.
I know the question is not nogeia anymore; this was just stam hocking. In the event that a real shaila should occur just go to a rav he should have no problem being mattir your neder/shevua.