Schwarber, batting fifth and playing in left field, went 0-for-4 with two strikeouts in the Cubs' 11-2 loss.
"I really just focused on myself and everything about my swing,'' Schwarber said Thursday about his stint in Iowa. "We'll see how it goes, but I'm planning on this being me and going out and competing.''
He added: "I'm ready to clean the slate and get back to business."
The 24-year-old Schwarber played 11 games for Iowa, hitting .343 with four home runsafter being demoted in late June.
"He looked right, and it was the right time to bring him back," manager Joe Maddon said.
Cubs president Theo Epstein said Schwarber's time in the minors was "more of a reset than a rebuilding" and that he looked better at the plate after hitting .171 in 64 games before being sent down.
"He was using the whole field more," Epstein said. "His last swing, he drove a ball off the wall in left-center. Kind of a classic Schwarber swing. He's ready to go."
On Wednesday, Maddon indicated Schwarber could return to the leadoff role but also said he liked Jon Jay batting first when the Cubs face a right-handed pitcher.
To make room for Schwarber on the roster, John Lackey has been placed on the disabled list with plantar fasciitis, but a source told ESPN that the pitcher shouldn't miss any starts. Lackey pitched his final game of the first half of the season Wednesday.
The Cubs trail the Brewers by 4 games in the National League Central.