The Saracens pack conceded six scrum penalties against Ospreys in their European Champions Cup clash earlier this month, with Vunipola putting in a poor performance.
"I don't think the criticism has been unfair," he told the BBC on Sunday. "I've had to take a look at myself in the last couple of weeks and go back to the drawing board.
"A few games have gone away a bit from what we were trying to work on as a team, and scrums are becoming an even tougher battle now."
With his younger brother Billy out with a broken arm, Vunipola's ball-carrying skills have become even more important for England and the 27-year-old is working with coaches Ian Peel at Saracens and England's Neal Hatley to get back on track.
"Neal is constantly messaging me, coming down to the club," Vunipola added. "Little things, where you feel you're doing one thing right, but there are other small things you could be doing better."
(Reporting by Shrivathsa Sridhar in Bengaluru, editing by Pritha Sarkar)
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