Shulchan Arukh, Orach Chayim 341/שולחן ערוך·אורח חיים שמ״א

1Annulling Vows on Shabbat, 3 Seifim: We annul vows on Shabbat if the vows' content is relevant to a Shabbat necessity, like if someone vowed not to eat or drink. We do this even if he had the opportunity to annul them before Shabbat. The husband can annul his wife's vows even if they are not relevant to Shabbat, because if he does not annul them today, he will not ever be able to annul them.

2If someone swore to do some labor within some time period, and he had no chance to do it until the last day of the time period, if that last day is Shabbat and he has valid reasons to annul his vow, he may ask for its annulment even on Shabbat.

3It is the practice to annul vows in which the community swears off something even if the vow's content is not relevant to Shabbat (and see above at the end of chapter 306).