1. The order of the blessings of the Amidah was decreed by the “Anshei Knesses Hagedolah” (The men of the Great Assembly) with allusions from different biblical verses, and it follows that it is forbidden to change their order. If he erred and accidentally omitted one of the blessings, he must return to that blessing and continue according to correct order, and repeat even those blessings which he had already (erroneously) said. However, if he omitted a blessing deliberately, he must return to the beginning of the Amidah and recommence. (Mishne Berurah 119)
2. If when in the middle of a blessing he noticed that he had erred in its words and he has not yet finished the blessing, he does not need to return to the beginning of the blessing. Instead, he must return only to the place where he had erred. (ibid)
