There isn't just one chapter that speaks of the Beast. There are a lot of verses about his mark.
Maybe the mark on the forehead refers to a lapse in judgment? Being beguiled to follow what the person doesn't realize is the Beast?
Like the woman who sold her forehead to a casino for ten thousand dollars so they could have tattooed there their casino .com address. A casino add on your face forever. For ten thousand dollars?
I looked and found a bunch to share here.
https://bible.knowing-jesus.com/topics/Mark-Of-The-Beast
Revelation 13:16-17
And he causes all, the small and the great, and the rich and the poor, and the free men and the slaves, to be given a mark on their right hand or on their forehead, and he provides that no one will be able to buy or to sell, except the one who has the mark, either the name of the beast or the number of his name.
Revelation 14:9-10
Then another angel, a third one, followed them, saying with a loud voice, “If anyone worships the beast and his image, and receives a mark on his forehead or on his hand, he also will drink of the wine of the wrath of God, which is mixed in full strength in the cup of His anger; and he will be tormented with fire and brimstone in the presence of the holy angels and in the presence of the Lamb.
Revelation 7:2
And I saw another angel ascending from the rising of the sun, having the seal of the living God; and he cried out with a loud voice to the four angels to whom it was granted to harm the earth and the sea,
Revelation 13:16
And he causes all, the small and the great, and the rich and the poor, and the free men and the slaves, to be given a mark on their right hand or on their forehead,
Revelation 13:17
and he provides that no one will be able to buy or to sell, except the one who has the mark, either the name of the beast or the number of his name.
Revelation 13:7-10
It was also given to him to make war with the saints and to overcome them, and authority over every tribe and people and tongue and nation was given to him. All who dwell on the earth will worship him, everyone whose name has not been written from the foundation of the world in the book of life of the Lamb who has been slain. If anyone has an ear, let him hear.read more.
Revelation 16:2
So the first angel went and poured out his bowl on the earth; and it became a loathsome and malignant sore on the people who had the mark of the beast and who worshiped his image.
Revelation 19:20
And the beast was seized, and with him the false prophet who performed the signs in his presence, by which he deceived those who had received the mark of the beast and those who worshiped his image; these two were thrown alive into the lake of fire which burns with brimstone.
Revelation 20:4
Then I saw thrones, and they sat on them, and judgment was given to them. And I saw the souls of those who had been beheaded because of their testimony of Jesus and because of the word of God, and those who had not worshiped the beast or his image, and had not received the mark on their forehead and on their hand; and they came to life and reigned with Christ for a thousand years.