"I will have to make a very small adjustment in his style of fighting," said Roach.
Pacquiao is currently in Baguio City for the first leg of his training camp.
Roach explained that someone told Pacquiao that Marquez does not have a good jab.
"That's a wrong notion. I told him that was wrong and what he was doing was wrong. I had to change his style a little and we will continue to change it this week," he said.
"I had to tell him Marquez is a good jabber. He is one of the best jabbers in boxing today," Roach added.
After seeing Pacquiao favoring his left hand, Roach instructed the Filipino champion to start using his right hand.
In his first 2 fights with Marquez, Pacquiao also used his left hand more. Both bouts ended in controversy, something Roach does not want to happen this time.
"That's what I don't want to happen: Manny falling back to what he'd been doing before, especially in their first 2 fights which did not impress many. I don't want a repeat of that," Roach said.
Even with the need for small changes in Pacquiao's style, Roach remains confident his fighter will convincingly defeat Marquez on November 12.
"Manny fought heavier, bigger opponents after that split decision victory in the second fight. He's stronger, faster and more mature now," he said.
Roach had previously predicted that the trilogy bout will not go past 6 rounds.