Why don’t we say a bracha on the mitzva of Hashuvas Aveida
There are a few reasons for this . One reason is because we don’t make a bracha on any mitzva that is dependant on someone else’s consent, such as giving tzedakah, returning a stolen item, mishloach manos, matanos l’evyonim or Hashovas Aveida, . When returning the lost item, the person returning it is dependant on the loser’s consent to actually take the item back, therefore we don’t make bracha on this mitzva.
Other reasons why we don’t make a bracha ono hashovas aveida, is because it could be that the person already gave up on getting the item baack, and therefore the person really doesn’t have to return it, therefore chazal said that we should not make a bracha on this mitzva at all. Another reason is because hashovas aveida is a “mitzva sichlis”- a mitzvah that we would understand intellectually on our own, and chazal didn’t institute that we make a bracha on such a mitzva.
Shiut Rashba 18, Shem Aryeh 1, Tumim 97, Sdei Chemed Mareches Brachos 767b, Har Tzvi parshas Ki Teitzei, Even Hatoen Baba Metzia 30 pg. 618.