Q. If one is certain that he is going to do teshuva on something wrong he did, does he make a bracha when making teshuva? What bracha? Does he say it when reciting viduy?
A. Beis Yitzchok (Nitzovim 193) maintains that although, teshuva is a positive mitzva, one does not recite a brocho on it, following the Rashbo’s opinion (Teshuvos 18) that one does not recite on a mitzva that came by an aveira, the sin he is now repenting from.
He adds that since teshuva could be accomplished with only a thought, as the Talmud (Kiddushin 49b) teaches, we don’t recite a blessing on “devarim shebalev” or just thoughts on ones heart, as Beis Yosef (434) asserts in regards to bitul chametz.
Likutei Shoshanim (p. 188) explains that since the mitzva is constant and without interruption, no brocho was dedicated for it. He also mentions that we actually already have a brocho for teshuva we recite three times a day in the amida. He adds another seven reasons, that include the doubts of future compliance.
Horav Shlomo Miller’s Shlit’a opinion is that, since as mentioned above, teshuva can be done with just a decision in one’s mind, he already complied with the mitzva immediately at that time, and the brocho would not be “over leasiyosso” before the mitzva is done, as is usually required.
Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a