It’s simple, she can’t. The time to contest the results of the election was right up to the point where she conceded, and the results of the election were certified in December.
No do-overs hitlery, you had your chance.
That’s it, you are right. Any contesting of an election has to have happened back then, not now. And any contesting has to be done with the election within any of the 50 states plus DC which choose electors to the electoral college.
This reminds us all, that there are actually 51 different elections on election day, held in each of the 50 states plus DC, as they choose electors to the electoral college.
The real election happens when the electors choose the president. The Congress certified the results of the electoral vote. That’s it. There is no way to contest a presidential election due to some amorphous notion that “Russia interfered”.