No, fallen angels cannot repent.  They have been given over to their sinful rebellion.  Repentance is something granted by God to people (2 Timothy 2:25) and is part of the act of salvation that is the work of God.  Angels have no way of being redeemed that we know of because the pattern of redemption involves the incarnation of God where he became one of us and died for us. This means we are able to be redeemed by the sacrifice of Christ, God in flesh (John 1:1, 14; Colossians 2:9).  But there is no such redemptive work supplied to the angelic realm.  Therefore, there is no regeneration and no change, which means no repentance. Thus, again, angels cannot repent.

The Bible speaks of elect angels or chosen angels.  “I solemnly charge you in the presence of God and of Christ Jesus and of His chosen angels, to maintain these principles without bias, doing nothing in a spirit of partiality,” (1 Timothy 5:21).  So we can see there were chosen angels.  This probably means that God elected angels not to fall in the great spiritual rebellion before the creation of the world.  Some believe that Revelation has a clue to the fall of the angels in the following verse.

Revelation 12:4, “And his tail swept away a third of the stars of heaven and threw them to the earth. And the dragon stood before the woman who was about to give birth, so that when she gave birth he might devour her child.”

If angels were chosen to not fall, it was probably for a reason to serve God.  We as humans have all fallen.  However, we have been chosen for redemption by God’s grace(2 Thessalonians 2:13; Ephesians 1:4-5).

So, fallen angels cannot repent, be saved, and spend eternity with God.  They knew God in the spiritual realm, rejected him, and will face their just punishment since they have no means of their sin being atoned for.