The turnaround came after Trump Friday he said he was planning to ban the Chinese-owned video app's U.S. operations as soon as Saturday after dismissing a possible sale to Microsoft.
Reuters reported last week that some investors are valuing TikTok at about $50 billion, citing people familiar with the matter.
"I did say that if you buy it, whatever the price is that goes to whoever owns it, because I guess it’s China essentially … I said a very substantial portion of that price is going to have to come into the Treasury of the United States because we’re making it possible for this deal to happen," Trump said.
It was not clear how the U.S. government would receive part of the purchase price.
He added it "will close down on September 15 unless Microsoft or somebody else is able to buy it and work out a deal, an appropriate deal so the Treasury … of the United States gets a lot of money.