1) 1) A person who, when praying the Amidah of Shabbos, erred and said the weekday version of the Amidah, and on top of that he erred a second time and did not say “Vesein Tal Umatar Livrachah”, some say that he should repeat from “Attah Chonein” until “Bareich Aleinu” and say the request of “Vesein Tal Umatar Livrachah”, and then say the Shabbos blessings of the Amidah, and others say that he does not repeat at all, but just finishes whichever blessing he is in the middle of saying, and follows immediately with the blessings of Shabbos. The custom is to follow the second opinion.
2) One who erred in his prayer and does not remember the law, should not ask someone by speaking as this would constitute an interruption. Instead, he should go to a place where there are books of Halachah and check there. If the place where he had commenced his prayer is his fixed place for praying, he should return there, but if it is not his fixed place, he should finish his prayer in the place where he checked the law. (Latter authorities)