The Lord gives a terse answer. It is two words in Hebrew: Judah first.
That makes sense. Judah’s leadership was especially appropriate at this time because that was the tribe of the murdered concubine. But unlike at the start of the book (Judges 1:2), the Lord does not promise victory.
18 The people of Israel arose and went up to Bethel and inquired of God, “Who shall go up first for us to fight against the people of Benjamin?” And the LORD said, “Judah shall go up first.”