Hebrews 12:23 reads: the assembly (ekklesia) of the firstborn who are enrolled in heaven.
With firstborn, the author means the beloved people of God and heirs: God chooses them, from everywhere. Their names are written down in heaven: this is how God personally knows us by name, we are not just numbers for him (Luke 10:20). As a citizen of heaven, you are enrolled on earth for a dwelling in heaven (Philippians 3:20). It is similar to a waiting list where you wait until a place becomes available. You look forward to that moment! Jesus has gone ahead of us to heaven, to reserve a nice place for us in his Father’s house with many rooms (John 14:2). When you die, God will bring you home.
23 and to the assembly of the firstborn who are enrolled in heaven, and to God, the judge of all, and to the spirits of the righteous made perfect,