Is it permitted to repeat an entire bracha of SE if one desires to do so (due to lack of kavana, or he didn’t say the words right in terms of how he pronounced them), or should one repeat only words within the bracha (prior to Baruch ata Hashem), but not the entire bracha?
If someone didn’t have kavana while davening SE if he is in middle of the first bracha, (which we are required to think the meaning of the words) he can go back to where he stopped having kavana, but if he already finished the bracha, he does not go back, however here are a few options. He can think the meaning of the bracha, and it is preferable for him to have kavana to the meaning of the words while saying the bracha of “Modim”, or if he is davening in shul he can wait and have kavana to when the chazan says it.
If he didn’t have kavana in one of the other brachos, or if he didn’t pronounce them correctly he is still yotza, and he does not go back, because since he was yotza repeated the bracha is a “bracha seino tzreicha”, (an unnecessary bracha) which is not allowed.
S:A O:CH 101-1 M:B ibid 4, Biur Halacha D:H V’haedna, Halichos Shlomo Tefilloh chap. 8 -9 ftnt. 4, M:B 68-1,