There are various verses in the Bible that say that God does not repent (Numbers 23:19: 1 Samuel 15:29), and then there are others which describe God repenting (Genesis 6:6-7, Exodus 32:13-14: 1 Samuel 2:30-31, 15:35, Amos 7:3, Jonah 3:10).

For instance:

Numbers 23:19

19 God is not a man, that he should lie; neither the son of man, that he should repent: hath he said, and shall he not do it? or hath he spoken, and shall he not make it good?

Genesis 6:6-7

6 And it repented the Lord that he had made man on the earth, and it grieved him at his heart.
7 And the Lord said, I will destroy man whom I have created from the face of the earth; both man, and beast, and the creeping thing, and the fowls of the air; for it repenteth me that I have made them.

From the above, notice that the point of the passage from Numbers, and the similar passage in 1 Samuel 15:29, is to establish that God does not lie (Titus 1:2, Hebrews 6:18). That is to say, He's not like a man, who makes a promise, and then changes his mind, and doesn't follow through on his word. That's the sense of the word "repent" being used in those verses.

Then, in all the verses that speak about God repenting, we have the sense of the word expressing God turning from what He had purposed or proposed to do prior, none of which was unconditional. He never broke His word to anyone, in any of the circumstances where He repents. He simply changed His mind, based on what took place.

This is because "repent", like thousands of words, can have more than one meaning. Context determines what sense of "repenting" is being used, and we are being told that in the negative, dishonest sense of the word, God does not repent.