Bike won't shift into 2 largest rear cogs (lowest gears)
I didn't see the video but if your talking about the last 2 lower gears you may need to loose the tension cable. if its the top 2 big gears then you may need to tighten.

make sure you derailleur is installed correctly. make sure the last pulley lines up at all cogs especially the biggest one, using your hand and pushing this up and down the cassette, make sure it clears.

try to unbolt the cable, back out on the gears with shifter and back out the fine tune barrel adjuster located on cable/derailleur. pedal, then chain should drop to last small cog. then pull cable hand tight and screw bolt back on cable. make any fine tuning with the barrel adjuster when shifting up.

those are some tips from what I would assume...maybe others can help :)