Was the immersion in water by the hand of others, a part of joining Christianity?

Was the immersion in water by **the hand/s of others** (such as the pastor's) for joining Christianity, *already practiced* in the time of Jesus in Judea (or right after), or was it something relatively new? I am trying to find what was the origin of the practice of the immersion with the help of other people, shown either in the New Testament or in the writings of the early church. (Please, see many examples here) N.b. My question is not about immersion in water, but about the help of others (by hands), while imersing. (Please, see here many examples of what I mean).