hi my friend, that is an excellent question. You are very observant. I had never noticed this difference before. So, here's what I have learned.
This same thing happens in Job 1:5 ("Perhaps my children have sinned and cursed [blessed] God in their heart"), Job 1:11 ("he will curse [bless] you to your face"), and again in Job 2:5. It is used in a similar way in Psalm 10:3, "the greedy man curses [blesses] and spurns the Lord".
Whatever the word means, it's obvious that this word is being used in a 'bad' / negative way here. It's something that Job does not want his children to do. It is something that Satan does want Job to do. It is something that Satan knows will displease God. So, Job's wife is telling Job to do what Satan wants him to do.
So, why does the Bible use the word normally translated "bless"? So far, I have found two possible explanations. The first is that the men who copied the ancient Old Testament (Hebrew) texts were fearful of writing the words "curse God". So they substituted the opposite word ("bless") knowing that people would realize this was not the right word, and understand the correct meaning from the context.
The second possibility is that by "bless" they mean "say good-bye". There is a relation between 'blessings' and greetings of welcome or farewell. In English, for example, "good bye" literally means "God be with you". So it may be that Satan wanted Job to say to God, "I am leaving you now, I don't want to be with you anymore, bye!" You have asked a good question and I hope this helped some.I am grateful that there are so many online reference tools available to help with questions like this.