John 4:1-6 gives the background to the next event, Jesus' conversation with a Samaritan woman. (See: rc://en/ta/man/translate/writing-background)
Now when Jesus knew that the Pharisees had heard that he was making ... John (although ... were), he left ... Galilee
"Now Jesus was making ... John (although ... were), and the Pharisees had heard about the success he was having. He learned that the Pharisees had heard, so he left ... Galilee"
Now when Jesus knew
The word "now" is used here to mark a break in the main events. Here John starts to tell a new part of the narrative.
Jesus himself was not baptizing
The reflexive pronoun "himself" adds emphasis that it was not Jesus who was baptizing, but his disciples. (See: rc://en/ta/man/translate/figs-rpronouns)