120:2 If someone forgot to count the entire night (or if he discovered that he counted the wrong day the night before – MB 489:35), he should count the next day without a bracha, then resume counting on the following night with a bracha. If he also forgot to count during the day, he should continue to count the rest of the nights without a bracha. If one is not sure whether or not he counted at night, he can count the rest of the nights with a bracha, even if he did not count during the day. (When one cannot say the bracha himself, he should make sure to hear another person say it and to answer “amen” with the intention to fulfill his obligation – MB 489:37.)
120:3 If one is asked by another person at twilight or later what day of the Omer is, he should reply, “Yesterday was such-and-such day.” If he tells the other person what day of the Omer it us, he may no longer count that night with a bracha.