This was done by either flicking the 2600 power switch on and off rapidly or sometimes merely inserting or removing a cartridge with the power on, weird glitches and effects caused by power fluctuations. I was reminded of this after just watching this video by no swear gamer on youtube.
lol, for better or worse I use to FRY my 2600 games continuously back in the day, honestly was not even aware of the term frying, thought it was a silly thing I discovered myself, no doubt many thought that. In Firefighter I think it was called? Got my fireman stuck in the building with no victims to rescue, you could get some odd effects flicking the power switch. Used to get similar effects on Colecovision running a butter knife along the terminals of the expansion port...now THAT might have just been me.