Military is the only way.

A legally appointed Commander in Chief existed up until exactly noon today (Jan 20, 2021). Up until then, they could only act on Trump's orders.

However, at exactly noon, authority transfers to a new President, "IF" one legally exists.

BUT, if the military knows a President was illegally sworn in, are they obligated to obey? No, because their oath is to the Constitution to protect the country and the people from threats both foreign and domestic.

So, at exactly noon, the military, for the first time, has independent authority to BEGIN certain actions,