kaz-k wrote:
1. Hi,
Shut down the Mac.
2. Open bottom case.
3. Remove battery cable from logic board.
Press and hold the power1. button for at least five seconds.
2. Connect battery cable to logic board.
3. Close bottom case.
4. Turn on the Mac.
Or if you have USB wired external keyboard and USB-C to USB adapter, connect them to your MacBook Pro and hold "Shift-Control-Option and power button" could works.
The SMC reset will only work on the internal laptop keyboard. It will not work from an external keyboard even if it is USB.
I don't recommend an inexperienced user opening up a 2016+ laptop because it is much more difficult to remove the bottom case than the older models. Plus it is easy to break the latching mechanism holding the battery cable in place. It can also be a little tricky reinstalling the bottom case.
Whether unauthorized opening of the laptop will void the warranty may vary by region. In the US you "should" be Ok, but if the user causes any damage to the laptop the damage will not be repaired under warranty and the user will need to pay. The parts on these laptops are very expensive.
Since the shift key does not work, why not take advantage of the free Apple Keyboard Repair Program?
https://support.apple.com/en-us/keyboard-service-program-for-mac-notebooks