He is expected to spend Saturday night in Las Vegas, Nevada, and then swing through western states.
Trump repeated a vow to bring most U.S. troops home from Afghanistan soon as part of his bid to halt "endless wars." The promise has raised concerns within the Afghan government that a US pullout could leave the country more vulnerable to the Taliban.
"We're almost finished in Afghanistan coming in," he said, adding that he wanted the troops reduced "down to a small number coming home by the end of the year - hopefully the end of the year, shortly thereafter."
Trump on Wednesday pulled into a statistical tie with Biden in hotly-contested Florida at 47% vs 49% with a credibility interval of four points, a Reuters/Ipsos opinion poll showed, though Biden had a 10 percentage point advantage nationally among likely voters.
On Thursday, Trump and Biden, who had been due to hold a second presidential debate, will instead take part in dueling televised town halls. NBC News said Trump's event in Miami would take place outdoors to prevent the spread of the coronavirus.
Biden's ABC News event will take place in Philadelphia.
That Trump, who fell ill with the virus earlier this month, is traveling to Iowa so close to Election Day suggests his campaign is concerned about voter support there for his re-election. Trump beat Democrat Hillary Clinton in the state by almost 10 percentage points in 2016, but opinion polls have shown Iowa to be competitive.
Nearly 15 million Americans have cast ballots, setting a record early pace, according to the US Elections Project at the University of Florida. Many are seeking to avoid the large crowds expected on Election Day.
In the last presidential election, some 1.4 million Americans had cast early votes as of Oct. 16, 2016.
Iowa has experienced a spike in Covid-19 cases, with hospitalisations at an all-time high. Republican Governor Kim Reynolds has resisted any statewide containment measures such as a mandate to wear masks and urged Trump supporters on social media to turn out en masse for the president.