If one forgets “nachem” at minchah on the fast of Tisha B’Av, one should say it in retzei, in the place of “yaaleh v’yavo.” But the ending of the berachah should be the regular one (“v’sechezenoh ainaiynu …hamachazir shechinasso…”).
One who is not fasting also says “nacheim”. One who must eat on the fast day, and is bentching, says “nacheim” before the words “uv’nei Yerushalayim,” with the ending being the regular one (“u’v’nei Yerushalayim…bonei b’rachamav…”).
After the fast, one may not eat until making havdala. A woman should make havdala for herself rather than eating before havdala. One may drink water before havdala. Havdala may be made over wine.