In 1 Cor. 6:2-3:
1Co 6:2 Do ye not know that the saints shall judge the world? and if the world shall be judged by you, are ye unworthy to judge the smallest matters?
1Co 6:3 Know ye not that we shall judge angels? how much more things that pertain to this life?
We read of God's people, during the 1,000 years in Heaven, Dan. 7:22; Rev. 20:4, judging not only the wicked upon the earth (who will all be dead and in the dust of the earth at that time; Isa. 24:22), but also the fallen angels (who will be bound that whole time on the broken down earth; Rev. 20:1-3, unable to leave). The judging, by the saints, takes place by going through the word of God, and Amen-ing God's punishments for sin, 2 Cor. 5:10, as each case is brought before them by what is written of them in the books of heaven; Isa. 65:6-7; that the finally impenitent receive their recompense in the earth, Pro. 11:31; Rev. 20:9; 2 Thes. 1:9, and thus when Jesus returns the third time with all the saints (Rev. 20; Isa. 24; Zec. 14, etc), then will the sentences obtained from the scripture, the word of God, Psa. 149:5-9, be carried out, Jud. 1:15, upon the impenitent who ever lived (of mankind) from the time of Cain to the last, and also including satan and his angels who sinned in Heaven. 2 Pet. 2:4; Eze. 28:15.
The evil angels, have not only sinned, but brought others to sin also, including the saints before they (the saints) being cleansed of all sin. The evil angels know of their time to come to be punished according to the word of God laid down for transgression (wages of sin is 2nd death, but each will receive according as they have done before they utterly perish into ashes forever; Eze. 28:19; Mal. 4:3, so that justice is met):
Mat_8:29 And, behold, they cried out, saying, What have we to do with thee, Jesus, thou Son of God? art thou come hither to torment us before the time?
God's people will know for certain that each of the cases brought before them became hopeless, and it is the duty of the congregation to judge, and agree with God's judgments for it, as Psa. 149 shows.