For example: Biden gets sworn in. Then, prior to Biden dismissing the the Trump cabinet, the Trump cabinet uses the 25th amendment to relieve Biden, Harris, and other members of Congress of their duties for high crimes and misdemeanors (treason, election fraud, crimes against humanity, etc.).
For Trump's statement, see 1:56 of https://rumble.com/vcpol3-president-trump-full-speech-delivers-remarks-in-alamo-tx-jan-12-2020.html
I think he meant them trying to fraudulently using the 25th remove a sitting president is treason and will bit them in the ass when the arrests start.