When states count the vote in a federal election they send a group of people called electors to the national congress. Those electors then cast that state's electoral votes according to state law (usually winner-take-all but a couple states split proportionally). These people falsely claimed to be the electors from Michigan, selected according to Michigan law, and they intended to infiltrate the meeting of the electoral college and fraudulently cast Michigan's electoral votes for Trump, who lost the state of Michigan in a free and fair election and was, by Michigan law, entitled to zero electoral votes. In doing so they also intended to deny Joe Biden the electoral votes of Michigan, which he had rightfully earned by winning a free and fair election.
Based on the article's admittedly poorly-wordered description, it sounds like the former. I think they were the would-be electors had Trump won the state -- when called to the state's GOP HQ, they signed a document claiming to have met in the state capitol, though they had not. When that certificate was submitted, that's when the alleged fraud took place.