Trump was thrilled to see his followers push through barriers, overwhelm an unprepared police force, and take the Capitol by storm. As insurgents roamed the halls of Congress hoping to turn lawmakers hostage and Trump supporters dropped the American flag to hoist his own banner, Trump strolled excitedly around the White House. The fact that other people didn't see this as a good thing completely puzzled him. It was exactly what Trump had wanted for years, after all.
As the New York Times reports, after a stunned nation withdrew in disgust and challenged Joe Biden for Trump to end this rampage by his supporters, Trump went to Twitter for a brief statement – one in which he kept the insurgents away were "very special" and assured them "I love you". Even so, Trump contained a statement that the violent criminals who were already smearing human excrement in the halls of Congress at the time should "go home in peace."
It's the last part Trump regrets. The part where he told them to leave and gave a hint that he would allow an orderly transition – but without naming Biden or including the word "peaceful".
At the end of a week of his supporters attempting to violently overthrow the American government, Trump only regrets that it didn't work. And after planning to pull in every white supremacist he could find and push them toward Congress, he did nothing more to cheer their victory.