We are born again through our participation in Jesus's death and resurrection in baptism. Ref Romans 6 v 1-11, Colossians 2, 1 Peter 3.

The examples that we have from the early church in Acts (and apocryphal history) show that baptism is done by full submersion (burial) and is more than just symbolic or "an outward sign of an inward transformation". Peter clearly states in Acts Chapter 2 that baptism washes alway sins (since it is participation in Jesus's death) and we receive the gift of the Holy Spirit through baptism. Baptism is not man's work, but rather God's offer and the work was done by Jesus.