The Laws of Prayer (The morning services) (27)

1. One who commenced the Amidah and became confused in the middle of his prayer and does not know how to continue, may walk to a place where he knows that there is a prayer-book and take it from there. (Shulchan Aruch and Mishne Berurah 96)

2. One who knows before praying that in the middle of his prayers he is going to need to find another place in his prayer-book, should mark the places that he is going to need, prior to the commencement of the prayers, so that he does not need to stop in the middle of the prayers and search for them. (ibid)