With apologies for only responding to your question at the "11th hour" I submit this account which may be relevant:
Directly after the Holy Spirit came upon the disciples in Jerusalem at Pentecost, there is an account of how Peter, who was filled with the Holy Spirit, was enabled to witness to the High Priest and other ruler and elders. It's in Acts chapter 4. Later, we hear that Stephen:
a man full of God's grace and power, did great wonders and miraculous signs among the people (Acts 6:8).
Yet he was stoned to death because of his witness and testimony to Christ Jesus:
But Stephen, full of the Holy Spirit, looked up to heaven and saw the glory of God, and Jesus standing at the right hand of God... While they were stoning him, Stephen prayed, 'Lord Jesus, receive my spirit.' Then he fell on his knees and cried out, 'Lord, do not hold this sin against them.'" (Acts 7:54-60)
The point is that it is the Holy Spirit who indwells the believer who enables them to speak, to pray, to live for the glory of God. There is no formula. There is no manual, or method. The early Christians just did it because they were filled with the Holy Spirit. They couldn't have done otherwise!
Here is another example of what it means to pray in the spirit.
Polycarp of Smyrna, Second Century: Both Irenaeus and Tertullian record that Polycarp had been a disciple of John the Apostle, one of Jesus’s disciples. In ‘On Illustrious Men’, Jerome writes that Polycarp was a disciple of John the Apostle and that John had ordained him as a bishop of Smyrna. Polycarp is regarded as one of three chief Apostolic Fathers, along with Clement of Rome and Ignatius of Antioch. https://en.wikipedia.org/wiki/Polycarp
Perhaps the best way to understand how the early Church viewed praying in the Spirit is to give an example. Given the terrible manner in which Polycarp was put to death, this prayer illustrates how a spirit-filled Christian can lift his eyes to heaven and, in spite of everything he is experiencing, can give praise and thanks to God as he is borne along by the power of the Holy Spirit.
A Dying Prayer of Polycarp, the Martyr
O Father of your well-beloved and blessed Son Jesus Christ, through whom we have known you, O God of the angels and powers and of every living creature, and of all sorts of righteous people which live in your presence, I thank you that you have graciously provided this day and this hour to allot me a portion among the number of martyrs, among the people of Christ to the resurrection of eternal life, both of body and soul, in the incorruption of the Holy Spirit.
Among them I will be received in your sight this day as a fruitful and acceptable sacrifice, you have already prepared, often revealed and now fulfilled. You are the most faithful God who cannot lie.
For all these things I praise you, I bless you, I glorify you; through the eternal High Priest, Jesus Christ, your well-beloved Son, to whom with you and the Holy Spirit, be all glory, now and forever. Amen.
That's an example of what it means to "pray in the Spirit".