899. Magen Avos, Zachreinu

129:4 In the Shabbos evening service, in “Magen Avos,” we likewise say “haMelech hakadosh” rather than “ha(k)Eil hakadosh.” If the shaliach tzibbur erred and said “ha(k)Eil hakadosh,” then if he immediately realized it, he goes back and says “haMelech hakadosh.” After this, he cannot go back. (Some say this is only if he concluded the bracha but that if he has not yet concluded it, he may go back – Mishnah Brurah 582:10.)

129:5 If one forgot to add the insertions “zachreinu” (“remember us”), “mi kamocha” (“who is like You”), “u’ksov” (“inscribe”) or “b’sefer chaim” (“in the book of life”), and he only realized after saying “Baruch Atah Hashem,” then, since he has said G-d’s Name, he finishes the bracha and continues praying as usual, without going back. If one forgot “u’b’chein tein pachdcha (“therefore, put Your awe”) and he finished “haMelech hakadosh,” then even if he has only said ‘”Baruch Atah Hashem,” he finishes “haMelech hakadosh” and proceeds with “Atah bachartanu” (“You have chosen us”).