Have a look in your BIOS and see if there are any options to select which GPU you want to use.
You can also use the glxinfo command to find more info on which GPU is running the show. See here:
Explore options to check and monitor the active video card of a Linux system.
www.baeldung.com
Before you give the Last Resort a try d-message the driver of the GPU if you think the driver isn't loading.
Drivers are listed under lsmod.
The Xorg log is helpful too- Just run this command to see what's going on.
Last Resort: You could blacklist the driver for the GPU that you don't want to run the show.
USE Caution here!
IF you decide to do that write down what you did so you can re-enable it again if you have to.
If the driver for the GPU that you didn't blacklist is not loading as it should: the screen will most likely stay black.