What could such a plan be? I don't know, I am not a US legal scholar nor expert in US politics.
Some inspiration is here:
https://www.qasimrashid.com/p/how-joe-biden-can-still-slow-maga
I am pretty certain that other competent people have come up with other elements of such a plan and more ideas for immediate actions that can be taken.
Point is, there is always something that can be done.
And the Biden administration has two months to do it.
Question remains: did they treat their own warnings about Trump seriously.