How can I fix CPU/GPU temp over 120 C?

First your system does not offer a separate dedicated GPU! Only the 15” models offer it.

Here’s a view of your logic board:

I’m not sure what the person who worked on your system did but replacing the CPU/GPU is really not doable without the correct gear. Swapping out the chip from another board doesn’t make sense. Getting the chip is just not possible as Intel only sold canes of 25 chips and no longer available from Intel or local suppliers. If the CPU/GPU where truly bad I would have just replaced the logic board.

So let’s start with the basics I would have done. First cleaning the fan & system of dust build up. I would have also replaced the HD SATA cable (yes high temp issues are often related) MacBook Pro 13" Unibody (Mid 2012) Hard Drive Cable. Make sure you apply a strip of electricians tape in the uppercase and use a Bic pen ink tube or bamboo skewer curl the cable so you don’t crease the corner bends following this guide MacBook Pro 13" Unibody Mid 2012 Hard Drive Cable Replacement

Next given the systems age I would have cleaned the old thermal paste and applied a fresh coat (Arctic Silver) I would have then monitored the heatsinks ability to move the heat using a non contact thermometer as the system warms up. Depending on what I see the heatsink maybe bad MacBook Pro 13" Unibody Mid 2012 Heat Sink Replacement

Monitoring your system is important but the level of information is also important. I’m more interested in high water marks and logging which this app won’t show you. Seeing things in a more graphical view I also think is better like how TG Pro works.

Lastly, you need to undo the damage you caused by removing the kext file, hopefully you can place it back other wise you’ll need to delete the system folder and install a fresh OS. I’ve had issues after someone has pulled a kext file trying to just re-install the OS on top.

As far as the sound we’ll need to first get this far before we look into it.